swift-promise

====================

一个Promise A+规范的实现,promise的介绍,请 点击

详细的实现原理

本实现完全遵循Promise A+规范,全部实现Promise A+测试用例

运行npm test可看到效果

Usage使用方法

var getJSON = function(url) {
  var promise = new Promise(function(resolve, reject){
    var client = new XMLHttpRequest();
    client.open("GET", url);
    client.onreadystatechange = handler;
    client.responseType = "json";
    client.setRequestHeader("Accept", "application/json");
    client.send();

    function handler() {
      if (this.readyState === this.DONE) {
        if (this.status === 200) { resolve(this.response); }
        else { reject(this); }
      }
    };
  });

  return promise;
};

getJSON("/posts.json").then(function(json) {
  // continue
}, function(error) {
  // handle errors
});

链式调用Chaining

var promise = new Promise(function (resolve, reject) {
        setTimeout(function(){
            resolve(100);
        },2000)
})

promise.then(function fn1(val){
    return val+100
}).then(function fn2(val){
    alert(val);
})

错误处理Error Handling

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

        setTimeout(function(){
            resolve(100);
        },2000)

})

promise.then(function fn1(val){
    return val+100
}).then(function fn2(val){
    alert(val);
}).catch(function(reason){
    
});
    

finally实例方法

无论promise兑现还是拒绝,都会执行,使用场景如某些ajax请求的loading界面最终会结束

var promise = new Promise(function (resolve, reject) {
        setTimeout(function(){
            resolve(100);
        },2000)

    })

promise.then(function fn1(val){
    return val+500;
})
.finally(function(result){ //result可能是履行的值或者抛出的异常
    //TODO
})
    

ES6中静态方法

Promise.resolve

Promise.resolve("abc")
    .then(function (val) {
        //val 为"abc"            
    })

            
var p = new Promise(function (resolve) {
    resolve("thenable");  
})

Promise
    .resolve(p)
    .then(function (val) {
      //val 为"thenable"            
    })
           

Promise.reject

Promise
    .reject("abc")
    .then(function (val) {}, function (reason) {
        alert(reason)//为"abc"
    })
    

Promise.all

var p = new Promise(function(resolve, reject) { resolve(3); });

Promise.all([true, p]).then(function(values) {
  // values == [ true, 3 ]
});

Promise.race

var p1 = new Promise(function(resolve, reject) { setTimeout(resolve, 500, "one"); });
var p2 = new Promise(function(resolve, reject) { setTimeout(resolve, 100, "two"); });

Promise.race([p1, p2]).then(function(value) {
  // value === "two"
});

var p3 = new Promise(function(resolve, reject) { setTimeout(resolve, 100, "three"); });
var p4 = new Promise(function(resolve, reject) { setTimeout(reject, 500, "four"); });

Promise.race([p3, p4]).then(function(value) {
  // value === "three"               
}, function(reason) {
  // Not called
});

var p5 = new Promise(function(resolve, reject) { setTimeout(resolve, 500, "five"); });
var p6 = new Promise(function(resolve, reject) { setTimeout(reject, 100, "six"); });

Promise.race([p5, p6]).then(function(value) {
  // Not called              
}, function(reason) {
  // reason === "six"
});