9

我想在不使用 jQuery 的情况下实现基本的 Deferred 对象。在这里，我将仅使用解决和拒绝功能实现完成和失败回调。promise当然，方法与此功能相关联。

我正在纯 js 中执行以下实现（已编辑）：

function Deferred() {
    var d = {};
    d.resolve = function() {
        d.done(arguments);
    }
    d.reject = function() {
        d.fail(arguments);
    }
    d.promise = function() {
        var x = {};
        x.done = function(args) {
            return args;
        }
        x.fail = function(args) {
            return args;
        }
        return x;
    }
    return d;
}


var v;

var setVal = function() {
    var d = new Deferred();
    setTimeout(function() {
        v = 'a value';
        d.resolve(this);
    }, 5000);
    return d.promise();
};

setVal().done(function() {
    console.log('all done :' + v);
});

但上面给出了错误：Object #<Object> has no method 'fail'

我知道Deferred()函数的返回对象“d”没有方法 done()。如果我从中返回 d.promiseDeferred()将没有解决和拒绝功能。

请指出我为实现延迟对象的简单目标而犯了什么错误。

这是我正在做的小提琴：http: //jsfiddle.net/SyEmK/14/

4

3 回答 3

21 
function Deferred(){
  this._done = [];
  this._fail = [];
}
Deferred.prototype = {
  execute: function(list, args){
    var i = list.length;

    // convert arguments to an array
    // so they can be sent to the
    // callbacks via the apply method
    args = Array.prototype.slice.call(args);

    while(i--) list[i].apply(null, args);
  },
  resolve: function(){
    this.execute(this._done, arguments);
  },
  reject: function(){
    this.execute(this._fail, arguments);
  }, 
  done: function(callback){
    this._done.push(callback);
  },
  fail: function(callback){
    this._fail.push(callback);
  }  
}


var v;

var setVal = function() {
    var d = new Deferred();
    setTimeout(function() {
        v = 'a value';
        d.resolve(this);
    }, 5000);
    return d;
};

setVal().done(function() {
    console.log('all done :' + v);
});
于 2013-08-07T07:20:10.607 回答
1

我认为最好在调用回调后取消分配回调以避免内存泄漏，并立即执行稍后添加的回调。

function deferred() {
  let thens = []
  let catches = []

  let status
  let resolvedValue
  let rejectedError

  return {
    resolve: value => {
      status = 'resolved'
      resolvedValue = value
      thens.forEach(t => t(value))
      thens = [] // Avoid memleaks.
    },
    reject: error => {
      status = 'rejected'
      rejectedError = error
      catches.forEach(c => c(error))
      catches = [] // Avoid memleaks.
    },
    then: cb => {
      if (status === 'resolved') {
        cb(resolvedValue)
      } else {
        thens.unshift(cb)
      }
    },
    catch: cb => {
      if (status === 'rejected') {
        cb(rejectedError)
      } else {
        catches.unshift(cb)
      }
    },
  }
}

const d = deferred()

setTimeout(() => {
  d.resolve('good')
}, 1000)

// Will be called after 1s
d.then(value => console.log('#1 resolved!', value))

setTimeout(() => {
  // Will be called after 3s and executed right away as it's already resolved
  d.then(value => console.log('#2 resolved!', value))
}, 3000)

于 2020-07-24T03:49:54.283 回答
0

我从未使用过 jquery Deferred，但如果有人来这里寻找 angularjs $q.defer()的克隆，你所要做的就是这个

function Defer() {
    const self = this;
    self.promise = new Promise((resolve, reject) => {
        self.resolve = resolve;
        self.reject = reject;
    });
}

//use it like this
const deferred = new Defer();
//then call deferred.resolve(), deferred.reject() and use deferred.promise
于 2021-08-19T16:00:26.010 回答