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微信小程序,封装同步请求

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封装统一请求的目的:在请求时有时会返回不同的返回码进行不同的数据处理,比如:返回正常时,进行正常操作,如果返回了异常,那么就需要进行不同的处理了,由于每次请求都可能出现各种返回码,所以进行请求封装,进行统一异常处理。

在小程序中提供的请求:

wx.request({  

          url: url, 

           data: params,

            method: ‘POST‘, 

           header: {                ‘content-type‘: ‘application/x-www-form-urlencoded‘            },

            success: function (result){ 

   }})

 

默认是一个异步请求,我在封装时采用封装同步请求的方式。

在这里我使用了ES6中的 es6-promise,Promise的特点是同步操作,可以创建数个Promise对象,把需要同步的代码封装到Promise对象中 

   let promisevariable = new Promise(function (resolve, reject) { 

       wx.request({

            url: servser+url,

            data: params, 

           method: ‘POST‘, 

           header: {                ‘content-type‘: ‘application/x-www-form-urlencoded‘            }, 

           success: function (result){ 

               var status = result.statusCode; 

               if(status == 500){ 

                   //程序抛出异常

                   var exception = result.data.exception; 

                   var msg = result.data.message; 

                   var path = result.data.path;

                                           wx.showToast({

                        title: exception+"\r\n"+msg+"\n\r"+path, 

                       icon: ‘loading‘,

                        duration: 1000

                    }); 

                   resolve(null); 

                   return ;

                }

                if(status != 200){

                    //系统未知异常

                    var msg = result.data.error;  

                  var path = result.data.path;

                       wx.showToast({

                        title: msg+"\n\r"+path,

                        icon: ‘loading‘,

                        duration: 1000

                    });  

                  resolve(null);   

                 return ;          

      }                //自定义异常  

              var sta = result.data.status;

                if(sta != 200){

                    var msg = result.data.message; 

                   wx.showToast({ 

                       title: msg,   

                     icon: ‘loading‘,  

                      duration: 1000

                    });

                    resolve(null);

                    return ;

                }  

                              resolve(result);

//这里就是每个Promise对象的结果

            }

        }); 

   }); 

 

然后把该对象按顺序放到一个数组中,使用Promise提供的方法 Promise.all

Promise.all([数组对象]).then(function(values) { 

//这里就可以顺序执行并得到每个结果 

console.log(values);

});

---------------------

 

 


//引入Promise

var Promise = require(‘./es6-promise.auto.js‘);

//获取服务器地址

var servser = getApp().data.servsers;

console.log(servser);

//默认请求

function sendRequest(url,params){

   

    let promisevariable = new Promise(function (resolve, reject) {

        wx.request({

            url: servser+url,

            data: params,

            method: ‘POST‘,

            header: {

                ‘content-type‘: ‘application/x-www-form-urlencoded‘

            },

            success: function (result){

                var status = result.statusCode;

                if(status == 500){

                    //程序抛出异常

                    var exception = result.data.exception;

                    var msg = result.data.message;

                    var path = result.data.path;  

                   

                    wx.showToast({

                        title: exception+"\r\n"+msg+"\n\r"+path,

                        icon: ‘loading‘,

                        duration: 1000

                    });

                    resolve(null);

                    return ;

                }

                if(status != 200){

                    //系统未知异常

                    var msg = result.data.error;

                    var path = result.data.path;  

                    wx.showToast({

                        title: msg+"\n\r"+path,

                        icon: ‘loading‘,

                        duration: 1000

                    });

                    resolve(null);

                    return ;

                }

 

 

                //自定义异常

                var sta = result.data.status;

                if(sta != 200){

                    var msg = result.data.message;

                    wx.showToast({

                        title: msg,

                        icon: ‘loading‘,

                        duration: 1000

                    });

                    resolve(null);

                    return ;

                }

               

                resolve(result);

            }

        });

    });

    return promisevariable;

}

 

 

 

//暴露公共访问接口

module.exports = {

  sendRequest: sendRequest,//公布公共请求接口

}

 

 

 

使用:

 


 var url = "/home/test";

        var params = {msg: ‘哈哈哈‘}

        requestHandler.sendRequest(url,params).then(values => {

            console.log(values.data)

            this.setData({

                result : values.data

            });

        })

 

 

 

es6-promise.auto.js

 


/*!

 * @overview es6-promise - a tiny implementation of Promises/A+.

 * @copyright Copyright (c) 2014 Yehuda Katz, Tom Dale, Stefan Penner and contributors (Conversion to ES6 API by Jake Archibald)

 * @license   Licensed under MIT license

 *            See https://raw.githubusercontent.com/stefanpenner/es6-promise/master/LICENSE

 * @version   v4.2.4+314e4831

 */

 

(function (global, factory) {

 typeof exports === ‘object‘ && typeof module !== ‘undefined‘ ? module.exports = factory() :

 typeof define === ‘function‘ && define.amd ? define(factory) :

 (global.ES6Promise = factory());

}(this, (function () { ‘use strict‘;

 

function objectOrFunction(x) {

  var type = typeof x;

  return x !== null && (type === ‘object‘ || type === ‘function‘);

}

 

function isFunction(x) {

  return typeof x === ‘function‘;

}

 

 

 

var _isArray = void 0;

if (Array.isArray) {

  _isArray = Array.isArray;

} else {

  _isArray = function (x) {

    return Object.prototype.toString.call(x) === ‘[object Array]‘;

  };

}

 

var isArray = _isArray;

 

var len = 0;

var vertxNext = void 0;

var customSchedulerFn = void 0;

 

var asap = function asap(callback, arg) {

  queue[len] = callback;

  queue[len + 1] = arg;

  len += 2;

  if (len === 2) {

    // If len is 2, that means that we need to schedule an async flush.

    // If additional callbacks are queued before the queue is flushed, they

    // will be processed by this flush that we are scheduling.

    if (customSchedulerFn) {

      customSchedulerFn(flush);

    } else {

      scheduleFlush();

    }

  }

};

 

function setScheduler(scheduleFn) {

  customSchedulerFn = scheduleFn;

}

 

function setAsap(asapFn) {

  asap = asapFn;

}

 

var browserWindow = typeof window !== ‘undefined‘ ? window : undefined;

var browserGlobal = browserWindow || {};

var BrowserMutationObserver = browserGlobal.MutationObserver || browserGlobal.WebKitMutationObserver;

var isNode = typeof self === ‘undefined‘ && typeof process !== ‘undefined‘ && {}.toString.call(process) === ‘[object process]‘;

 

// test for web worker but not in IE10

var isWorker = typeof Uint8ClampedArray !== ‘undefined‘ && typeof importScripts !== ‘undefined‘ && typeof MessageChannel !== ‘undefined‘;

 

// node

function useNextTick() {

  // node version 0.10.x displays a deprecation warning when nextTick is used recursively

  // see https://github.com/cujojs/when/issues/410 for details

  return function () {

    return process.nextTick(flush);

  };

}

 

// vertx

function useVertxTimer() {

  if (typeof vertxNext !== ‘undefined‘) {

    return function () {

      vertxNext(flush);

    };

  }

 

  return useSetTimeout();

}

 

function useMutationObserver() {

  var iterations = 0;

  var observer = new BrowserMutationObserver(flush);

  var node = document.createTextNode(‘‘);

  observer.observe(node, { characterData: true });

 

  return function () {

    node.data = iterations = ++iterations % 2;

  };

}

 

// web worker

function useMessageChannel() {

  var channel = new MessageChannel();

  channel.port1.onmessage = flush;

  return function () {

    return channel.port2.postMessage(0);

  };

}

 

function useSetTimeout() {

  // Store setTimeout reference so es6-promise will be unaffected by

  // other code modifying setTimeout (like sinon.useFakeTimers())

  var globalSetTimeout = setTimeout;

  return function () {

    return globalSetTimeout(flush, 1);

  };

}

 

var queue = new Array(1000);

function flush() {

  for (var i = 0; i < len; i += 2) {

    var callback = queue[i];

    var arg = queue[i + 1];

 

    callback(arg);

 

    queue[i] = undefined;

    queue[i + 1] = undefined;

  }

 

  len = 0;

}

 

function attemptVertx() {

  try {

    var vertx = Function(‘return this‘)().require(‘vertx‘);

    vertxNext = vertx.runOnLoop || vertx.runOnContext;

    return useVertxTimer();

  } catch (e) {

    return useSetTimeout();

  }

}

 

var scheduleFlush = void 0;

// Decide what async method to use to triggering processing of queued callbacks:

if (isNode) {

  scheduleFlush = useNextTick();

} else if (BrowserMutationObserver) {

  scheduleFlush = useMutationObserver();

} else if (isWorker) {

  scheduleFlush = useMessageChannel();

} else if (browserWindow === undefined && typeof require === ‘function‘) {

  scheduleFlush = attemptVertx();

} else {

  scheduleFlush = useSetTimeout();

}

 

function then(onFulfillment, onRejection) {

  var parent = this;

 

  var child = new this.constructor(noop);

 

  if (child[PROMISE_ID] === undefined) {

    makePromise(child);

  }

 

  var _state = parent._state;

 

 

  if (_state) {

    var callback = arguments[_state - 1];

    asap(function () {

      return invokeCallback(_state, child, callback, parent._result);

    });

  } else {

    subscribe(parent, child, onFulfillment, onRejection);

  }

 

  return child;

}

 

/**

  `Promise.resolve` returns a promise that will become resolved with the

  passed `value`. It is shorthand for the following:

 

  ```javascript

  let promise = new Promise(function(resolve, reject){

    resolve(1);

  });

 

  promise.then(function(value){

    // value === 1

  });

  ```

 

  Instead of writing the above, your code now simply becomes the following:

 

  ```javascript

  let promise = Promise.resolve(1);

 

  promise.then(function(value){

    // value === 1

  });

  ```

 

  @method resolve

  @static

  @param {Any} value value that the returned promise will be resolved with

  Useful for tooling.

  @return {Promise} a promise that will become fulfilled with the given

  `value`

*/

function resolve$1(object) {

  /*jshint validthis:true */

  var Constructor = this;

 

  if (object && typeof object === ‘object‘ && object.constructor === Constructor) {

    return object;

  }

 

  var promise = new Constructor(noop);

  resolve(promise, object);

  return promise;

}

 

var PROMISE_ID = Math.random().toString(36).substring(2);

 

function noop() {}

 

var PENDING = void 0;

var FULFILLED = 1;

var REJECTED = 2;

 

var TRY_CATCH_ERROR = { error: null };

 

function selfFulfillment() {

  return new TypeError("You cannot resolve a promise with itself");

}

 

function cannotReturnOwn() {

  return new TypeError(‘A promises callback cannot return that same promise.‘);

}

 

function getThen(promise) {

  try {

    return promise.then;

  } catch (error) {

    TRY_CATCH_ERROR.error = error;

    return TRY_CATCH_ERROR;

  }

}

 

function tryThen(then$$1, value, fulfillmentHandler, rejectionHandler) {

  try {

    then$$1.call(value, fulfillmentHandler, rejectionHandler);

  } catch (e) {

    return e;

  }

}

 

function handleForeignThenable(promise, thenable, then$$1) {

  asap(function (promise) {

    var sealed = false;

    var error = tryThen(then$$1, thenable, function (value) {

      if (sealed) {

        return;

      }

      sealed = true;

      if (thenable !== value) {

        resolve(promise, value);

      } else {

        fulfill(promise, value);

      }

    }, function (reason) {

      if (sealed) {

        return;

      }

      sealed = true;

 

      reject(promise, reason);

    }, ‘Settle: ‘ + (promise._label || ‘ unknown promise‘));

 

    if (!sealed && error) {

      sealed = true;

      reject(promise, error);

    }

  }, promise);

}

 

function handleOwnThenable(promise, thenable) {

  if (thenable._state === FULFILLED) {

    fulfill(promise, thenable._result);

  } else if (thenable._state === REJECTED) {

    reject(promise, thenable._result);

  } else {

    subscribe(thenable, undefined, function (value) {

      return resolve(promise, value);

    }, function (reason) {

      return reject(promise, reason);

    });

  }

}

 

function handleMaybeThenable(promise, maybeThenable, then$$1) {

  if (maybeThenable.constructor === promise.constructor && then$$1 === then && maybeThenable.constructor.resolve === resolve$1) {

    handleOwnThenable(promise, maybeThenable);

  } else {

    if (then$$1 === TRY_CATCH_ERROR) {

      reject(promise, TRY_CATCH_ERROR.error);

      TRY_CATCH_ERROR.error = null;

    } else if (then$$1 === undefined) {

      fulfill(promise, maybeThenable);

    } else if (isFunction(then$$1)) {

      handleForeignThenable(promise, maybeThenable, then$$1);

    } else {

      fulfill(promise, maybeThenable);

    }

  }

}

 

function resolve(promise, value) {

  if (promise === value) {

    reject(promise, selfFulfillment());

  } else if (objectOrFunction(value)) {

    handleMaybeThenable(promise, value, getThen(value));

  } else {

    fulfill(promise, value);

  }

}

 

function publishRejection(promise) {

  if (promise._onerror) {

    promise._onerror(promise._result);

  }

 

  publish(promise);

}

 

function fulfill(promise, value) {

  if (promise._state !== PENDING) {

    return;

  }

 

  promise._result = value;

  promise._state = FULFILLED;

 

  if (promise._subscribers.length !== 0) {

    asap(publish, promise);

  }

}

 

function reject(promise, reason) {

  if (promise._state !== PENDING) {

    return;

  }

  promise._state = REJECTED;

  promise._result = reason;

 

  asap(publishRejection, promise);

}

 

function subscribe(parent, child, onFulfillment, onRejection) {

  var _subscribers = parent._subscribers;

  var length = _subscribers.length;

 

 

  parent._onerror = null;

 

  _subscribers[length] = child;

  _subscribers[length + FULFILLED] = onFulfillment;

  _subscribers[length + REJECTED] = onRejection;

 

  if (length === 0 && parent._state) {

    asap(publish, parent);

  }

}

 

function publish(promise) {

  var subscribers = promise._subscribers;

  var settled = promise._state;

 

  if (subscribers.length === 0) {

    return;

  }

 

  var child = void 0,

      callback = void 0,

      detail = promise._result;

 

  for (var i = 0; i < subscribers.length; i += 3) {

    child = subscribers[i];

    callback = subscribers[i + settled];

 

    if (child) {

      invokeCallback(settled, child, callback, detail);

    } else {

      callback(detail);

    }

  }

 

  promise._subscribers.length = 0;

}

 

function tryCatch(callback, detail) {

  try {

    return callback(detail);

  } catch (e) {

    TRY_CATCH_ERROR.error = e;

    return TRY_CATCH_ERROR;

  }

}

 

function invokeCallback(settled, promise, callback, detail) {

  var hasCallback = isFunction(callback),

      value = void 0,

      error = void 0,

      succeeded = void 0,

      failed = void 0;

 

  if (hasCallback) {

    value = tryCatch(callback, detail);

 

    if (value === TRY_CATCH_ERROR) {

      failed = true;

      error = value.error;

      value.error = null;

    } else {

      succeeded = true;

    }

 

    if (promise === value) {

      reject(promise, cannotReturnOwn());

      return;

    }

  } else {

    value = detail;

    succeeded = true;

  }

 

  if (promise._state !== PENDING) {

    // noop

  } else if (hasCallback && succeeded) {

    resolve(promise, value);

  } else if (failed) {

    reject(promise, error);

  } else if (settled === FULFILLED) {

    fulfill(promise, value);

  } else if (settled === REJECTED) {

    reject(promise, value);

  }

}

 

function initializePromise(promise, resolver) {

  try {

    resolver(function resolvePromise(value) {

      resolve(promise, value);

    }, function rejectPromise(reason) {

      reject(promise, reason);

    });

  } catch (e) {

    reject(promise, e);

  }

}

 

var id = 0;

function nextId() {

  return id++;

}

 

function makePromise(promise) {

  promise[PROMISE_ID] = id++;

  promise._state = undefined;

  promise._result = undefined;

  promise._subscribers = [];

}

 

function validationError() {

  return new Error(‘Array Methods must be provided an Array‘);

}

 

var Enumerator = function () {

  function Enumerator(Constructor, input) {

    this._instanceConstructor = Constructor;

    this.promise = new Constructor(noop);

 

    if (!this.promise[PROMISE_ID]) {

      makePromise(this.promise);

    }

 

    if (isArray(input)) {

      this.length = input.length;

      this._remaining = input.length;

 

      this._result = new Array(this.length);

 

      if (this.length === 0) {

        fulfill(this.promise, this._result);

      } else {

        this.length = this.length || 0;

        this._enumerate(input);

        if (this._remaining === 0) {

          fulfill(this.promise, this._result);

        }

      }

    } else {

      reject(this.promise, validationError());

    }

  }

 

  Enumerator.prototype._enumerate = function _enumerate(input) {

    for (var i = 0; this._state === PENDING && i < input.length; i++) {

      this._eachEntry(input[i], i);

    }

  };

 

  Enumerator.prototype._eachEntry = function _eachEntry(entry, i) {

    var c = this._instanceConstructor;

    var resolve$$1 = c.resolve;

 

 

    if (resolve$$1 === resolve$1) {

      var _then = getThen(entry);

 

      if (_then === then && entry._state !== PENDING) {

        this._settledAt(entry._state, i, entry._result);

      } else if (typeof _then !== ‘function‘) {

        this._remaining--;

        this._result[i] = entry;

      } else if (c === Promise$2) {

        var promise = new c(noop);

        handleMaybeThenable(promise, entry, _then);

        this._willSettleAt(promise, i);

      } else {

        this._willSettleAt(new c(function (resolve$$1) {

          return resolve$$1(entry);

        }), i);

      }

    } else {

      this._willSettleAt(resolve$$1(entry), i);

    }

  };

 

  Enumerator.prototype._settledAt = function _settledAt(state, i, value) {

    var promise = this.promise;

 

 

    if (promise._state === PENDING) {

      this._remaining--;

 

      if (state === REJECTED) {

        reject(promise, value);

      } else {

        this._result[i] = value;

      }

    }

 

    if (this._remaining === 0) {

      fulfill(promise, this._result);

    }

  };

 

  Enumerator.prototype._willSettleAt = function _willSettleAt(promise, i) {

    var enumerator = this;

 

    subscribe(promise, undefined, function (value) {

      return enumerator._settledAt(FULFILLED, i, value);

    }, function (reason) {

      return enumerator._settledAt(REJECTED, i, reason);

    });

  };

 

  return Enumerator;

}();

 

/**

  `Promise.all` accepts an array of promises, and returns a new promise which

  is fulfilled with an array of fulfillment values for the passed promises, or

  rejected with the reason of the first passed promise to be rejected. It casts all

  elements of the passed iterable to promises as it runs this algorithm.

 

  Example:

 

  ```javascript

  let promise1 = resolve(1);

  let promise2 = resolve(2);

  let promise3 = resolve(3);

  let promises = [ promise1, promise2, promise3 ];

 

  Promise.all(promises).then(function(array){

    // The array here would be [ 1, 2, 3 ];

  });

  ```

 

  If any of the `promises` given to `all` are rejected, the first promise

  that is rejected will be given as an argument to the returned promises‘s

  rejection handler. For example:

 

  Example:

 

  ```javascript

  let promise1 = resolve(1);

  let promise2 = reject(new Error("2"));

  let promise3 = reject(new Error("3"));

  let promises = [ promise1, promise2, promise3 ];

 

  Promise.all(promises).then(function(array){

    // Code here never runs because there are rejected promises!

  }, function(error) {

    // error.message === "2"

  });

  ```

 

  @method all

  @static

  @param {Array} entries array of promises

  @param {String} label optional string for labeling the promise.

  Useful for tooling.

  @return {Promise} promise that is fulfilled when all `promises` have been

  fulfilled, or rejected if any of them become rejected.

  @static

*/

function all(entries) {

  return new Enumerator(this, entries).promise;

}

 

/**

  `Promise.race` returns a new promise which is settled in the same way as the

  first passed promise to settle.

 

  Example:

 

  ```javascript

  let promise1 = new Promise(function(resolve, reject){

    setTimeout(function(){

      resolve(‘promise 1‘);

    }, 200);

  });

 

  let promise2 = new Promise(function(resolve, reject){

    setTimeout(function(){

      resolve(‘promise 2‘);

    }, 100);

  });

 

  Promise.race([promise1, promise2]).then(function(result){

    // result === ‘promise 2‘ because it was resolved before promise1

    // was resolved.

  });

  ```

 

  `Promise.race` is deterministic in that only the state of the first

  settled promise matters. For example, even if other promises given to the

  `promises` array argument are resolved, but the first settled promise has

  become rejected before the other promises became fulfilled, the returned

  promise will become rejected:

 

  ```javascript

  let promise1 = new Promise(function(resolve, reject){

    setTimeout(function(){

      resolve(‘promise 1‘);

    }, 200);

  });

 

  let promise2 = new Promise(function(resolve, reject){

    setTimeout(function(){

      reject(new Error(‘promise 2‘));

    }, 100);

  });

 

  Promise.race([promise1, promise2]).then(function(result){

    // Code here never runs

  }, function(reason){

    // reason.message === ‘promise 2‘ because promise 2 became rejected before

    // promise 1 became fulfilled

  });

  ```

 

  An example real-world use case is implementing timeouts:

 

  ```javascript

  Promise.race([ajax(‘foo.json‘), timeout(5000)])

  ```

 

  @method race

  @static

  @param {Array} promises array of promises to observe

  Useful for tooling.

  @return {Promise} a promise which settles in the same way as the first passed

  promise to settle.

*/

function race(entries) {

  /*jshint validthis:true */

  var Constructor = this;

 

  if (!isArray(entries)) {

    return new Constructor(function (_, reject) {

      return reject(new TypeError(‘You must pass an array to race.‘));

    });

  } else {

    return new Constructor(function (resolve, reject) {

      var length = entries.length;

      for (var i = 0; i < length; i++) {

        Constructor.resolve(entries[i]).then(resolve, reject);

      }

    });

  }

}

 

/**

  `Promise.reject` returns a promise rejected with the passed `reason`.

  It is shorthand for the following:

 

  ```javascript

  let promise = new Promise(function(resolve, reject){

    reject(new Error(‘WHOOPS‘));

  });

 

  promise.then(function(value){

    // Code here doesn‘t run because the promise is rejected!

  }, function(reason){

    // reason.message === ‘WHOOPS‘

  });

  ```

 

  Instead of writing the above, your code now simply becomes the following:

 

  ```javascript

  let promise = Promise.reject(new Error(‘WHOOPS‘));

 

  promise.then(function(value){

    // Code here doesn‘t run because the promise is rejected!

  }, function(reason){

    // reason.message === ‘WHOOPS‘

  });

  ```

 

  @method reject

  @static

  @param {Any} reason value that the returned promise will be rejected with.

  Useful for tooling.

  @return {Promise} a promise rejected with the given `reason`.

*/

function reject$1(reason) {

  /*jshint validthis:true */

  var Constructor = this;

  var promise = new Constructor(noop);

  reject(promise, reason);

  return promise;

}

 

function needsResolver() {

  throw new TypeError(‘You must pass a resolver function as the first argument to the promise constructor‘);

}

 

function needsNew() {

  throw new TypeError("Failed to construct ‘Promise‘: Please use the ‘new‘ operator, this object constructor cannot be called as a function.");

}

 

/**

  Promise objects represent the eventual result of an asynchronous operation. The

  primary way of interacting with a promise is through its `then` method, which

  registers callbacks to receive either a promise‘s eventual value or the reason

  why the promise cannot be fulfilled.

 

  Terminology

  -----------

 

  - `promise` is an object or function with a `then` method whose behavior conforms to this specification.

  - `thenable` is an object or function that defines a `then` method.

  - `value` is any legal JavaScript value (including undefined, a thenable, or a promise).

  - `exception` is a value that is thrown using the throw statement.

  - `reason` is a value that indicates why a promise was rejected.

  - `settled` the final resting state of a promise, fulfilled or rejected.

 

  A promise can be in one of three states: pending, fulfilled, or rejected.

 

  Promises that are fulfilled have a fulfillment value and are in the fulfilled

  state.  Promises that are rejected have a rejection reason and are in the

  rejected state.  A fulfillment value is never a thenable.

 

  Promises can also be said to *resolve* a value.  If this value is also a

  promise, then the original promise‘s settled state will match the value‘s

  settled state.  So a promise that *resolves* a promise that rejects will

  itself reject, and a promise that *resolves* a promise that fulfills will

  itself fulfill.

 

 

  Basic Usage:

  ------------

 

  ```js

  let promise = new Promise(function(resolve, reject) {

    // on success

    resolve(value);

 

    // on failure

    reject(reason);

  });

 

  promise.then(function(value) {

    // on fulfillment

  }, function(reason) {

    // on rejection

  });

  ```

 

  Advanced Usage:

  ---------------

 

  Promises shine when abstracting away asynchronous interactions such as

  `XMLHttpRequest`s.

 

  ```js

  function getJSON(url) {

    return new Promise(function(resolve, reject){

      let xhr = new XMLHttpRequest();

 

      xhr.open(‘GET‘, url);

      xhr.onreadystatechange = handler;

      xhr.responseType = ‘json‘;

      xhr.setRequestHeader(‘Accept‘, ‘application/json‘);

      xhr.send();

 

      function handler() {

        if (this.readyState === this.DONE) {

          if (this.status === 200) {

            resolve(this.response);

          } else {

            reject(new Error(‘getJSON: `‘ + url + ‘` failed with status: [‘ + this.status + ‘]‘));

          }

        }

      };

    });

  }

 

  getJSON(‘/posts.json‘).then(function(json) {

    // on fulfillment

  }, function(reason) {

    // on rejection

  });

  ```

 

  Unlike callbacks, promises are great composable primitives.

 

  ```js

  Promise.all([

    getJSON(‘/posts‘),

    getJSON(‘/comments‘)

  ]).then(function(values){

    values[0] // => postsJSON

    values[1] // => commentsJSON

 

    return values;

  });

  ```

 

  @class Promise

  @param {Function} resolver

  Useful for tooling.

  @constructor

*/

 

var Promise$2 = function () {

  function Promise(resolver) {

    this[PROMISE_ID] = nextId();

    this._result = this._state = undefined;

    this._subscribers = [];

 

    if (noop !== resolver) {

      typeof resolver !== ‘function‘ && needsResolver();

      this instanceof Promise ? initializePromise(this, resolver) : needsNew();

    }

  }

 

  /**

  The primary way of interacting with a promise is through its `then` method,

  which registers callbacks to receive either a promise‘s eventual value or the

  reason why the promise cannot be fulfilled.

   ```js

  findUser().then(function(user){

    // user is available

  }, function(reason){

    // user is unavailable, and you are given the reason why

  });

  ```

   Chaining

  --------

   The return value of `then` is itself a promise.  This second, ‘downstream‘

  promise is resolved with the return value of the first promise‘s fulfillment

  or rejection handler, or rejected if the handler throws an exception.

   ```js

  findUser().then(function (user) {

    return user.name;

  }, function (reason) {

    return ‘default name‘;

  }).then(function (userName) {

    // If `findUser` fulfilled, `userName` will be the user‘s name, otherwise it

    // will be `‘default name‘`

  });

   findUser().then(function (user) {

    throw new Error(‘Found user, but still unhappy‘);

  }, function (reason) {

    throw new Error(‘`findUser` rejected and we‘re unhappy‘);

  }).then(function (value) {

    // never reached

  }, function (reason) {

    // if `findUser` fulfilled, `reason` will be ‘Found user, but still unhappy‘.

    // If `findUser` rejected, `reason` will be ‘`findUser` rejected and we‘re unhappy‘.

  });

  ```

  If the downstream promise does not specify a rejection handler, rejection reasons will be propagated further downstream.

   ```js

  findUser().then(function (user) {

    throw new PedagogicalException(‘Upstream error‘);

  }).then(function (value) {

    // never reached

  }).then(function (value) {

    // never reached

  }, function (reason) {

    // The `PedgagocialException` is propagated all the way down to here

  });

  ```

   Assimilation

  ------------

   Sometimes the value you want to propagate to a downstream promise can only be

  retrieved asynchronously. This can be achieved by returning a promise in the

  fulfillment or rejection handler. The downstream promise will then be pending

  until the returned promise is settled. This is called *assimilation*.

   ```js

  findUser().then(function (user) {

    return findCommentsByAuthor(user);

  }).then(function (comments) {

    // The user‘s comments are now available

  });

  ```

   If the assimliated promise rejects, then the downstream promise will also reject.

   ```js

  findUser().then(function (user) {

    return findCommentsByAuthor(user);

  }).then(function (comments) {

    // If `findCommentsByAuthor` fulfills, we‘ll have the value here

  }, function (reason) {

    // If `findCommentsByAuthor` rejects, we‘ll have the reason here

  });

  ```

   Simple Example

  --------------

   Synchronous Example

   ```javascript

  let result;

   try {

    result = findResult();

    // success

  } catch(reason) {

    // failure

  }

  ```

   Errback Example

   ```js

  findResult(function(result, err){

    if (err) {

      // failure

    } else {

      // success

    }

  });

  ```

   Promise Example;

   ```javascript

  findResult().then(function(result){

    // success

  }, function(reason){

    // failure

  });

  ```

   Advanced Example

  --------------

   Synchronous Example

   ```javascript

  let author, books;

   try {

    author = findAuthor();

    books  = findBooksByAuthor(author);

    // success

  } catch(reason) {

    // failure

  }

  ```

   Errback Example

   ```js

   function foundBooks(books) {

   }

   function failure(reason) {

   }

   findAuthor(function(author, err){

    if (err) {

      failure(err);

      // failure

    } else {

      try {

        findBoooksByAuthor(author, function(books, err) {

          if (err) {

            failure(err);

          } else {

            try {

              foundBooks(books);

            } catch(reason) {

              failure(reason);

            }

          }

        });

      } catch(error) {

        failure(err);

      }

      // success

    }

  });

  ```

   Promise Example;

   ```javascript

  findAuthor().

    then(findBooksByAuthor).

    then(function(books){

      // found books

  }).catch(function(reason){

    // something went wrong

  });

  ```

   @method then

  @param {Function} onFulfilled

  @param {Function} onRejected

  Useful for tooling.

  @return {Promise}

  */

 

  /**

  `catch` is simply sugar for `then(undefined, onRejection)` which makes it the same

  as the catch block of a try/catch statement.

  ```js

  function findAuthor(){

  throw new Error(‘couldn‘t find that author‘);

  }

  // synchronous

  try {

  findAuthor();

  } catch(reason) {

  // something went wrong

  }

  // async with promises

  findAuthor().catch(function(reason){

  // something went wrong

  });

  ```

  @method catch

  @param {Function} onRejection

  Useful for tooling.

  @return {Promise}

  */

 

 

  Promise.prototype.catch = function _catch(onRejection) {

    return this.then(null, onRejection);

  };

 

  /**

    `finally` will be invoked regardless of the promise‘s fate just as native

    try/catch/finally behaves

 

    Synchronous example:

 

    ```js

    findAuthor() {

      if (Math.random() > 0.5) {

        throw new Error();

      }

      return new Author();

    }

 

    try {

      return findAuthor(); // succeed or fail

    } catch(error) {

      return findOtherAuther();

    } finally {

      // always runs

      // doesn‘t affect the return value

    }

    ```

 

    Asynchronous example:

 

    ```js

    findAuthor().catch(function(reason){

      return findOtherAuther();

    }).finally(function(){

      // author was either found, or not

    });

    ```

 

    @method finally

    @param {Function} callback

    @return {Promise}

  */

 

 

  Promise.prototype.finally = function _finally(callback) {

    var promise = this;

    var constructor = promise.constructor;

 

    return promise.then(function (value) {

      return constructor.resolve(callback()).then(function () {

        return value;

      });

    }, function (reason) {

      return constructor.resolve(callback()).then(function () {

        throw reason;

      });

    });

  };

 

  return Promise;

}();

 

Promise$2.prototype.then = then;

Promise$2.all = all;

Promise$2.race = race;

Promise$2.resolve = resolve$1;

Promise$2.reject = reject$1;

Promise$2._setScheduler = setScheduler;

Promise$2._setAsap = setAsap;

Promise$2._asap = asap;

 

/*global self*/

function polyfill() {

  var local = void 0;

 

  if (typeof global !== ‘undefined‘) {

    local = global;

  } else if (typeof self !== ‘undefined‘) {

    local = self;

  } else {

    try {

      local = Function(‘return this‘)();

    } catch (e) {

      throw new Error(‘polyfill failed because global object is unavailable in this environment‘);

    }

  }

 

  var P = local.Promise;

 

  if (P) {

    var promiseToString = null;

    try {

      promiseToString = Object.prototype.toString.call(P.resolve());

    } catch (e) {

      // silently ignored

    }

 

    if (promiseToString === ‘[object Promise]‘ && !P.cast) {

      return;

    }

  }

 

  local.Promise = Promise$2;

}

 

// Strange compat..

Promise$2.polyfill = polyfill;

Promise$2.Promise = Promise$2;

 

Promise$2.polyfill();

 

return Promise$2;

 

})));

 

 

 

//# sourceMappingURL=es6-promise.auto.map

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原文:https://www.cnblogs.com/gentrywolf/p/10115336.html

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