Promise的几个例子

setTimeout(function(){
            console.log(1)
        }, 0);
        new Promise(function excutor(resolve) {
            console.log(2);
            resolve()
            console.log(3)
        }).then(function(){
            console.log(4)
        })
        console.log(5)

• 输出23541

setTimeout(function(){
            console.log(1)
        }, 0);
        new Promise(function excutor(resolve) {
            console.log(2);
             for(var i = 0; i < 10000; i++) {
                i == 999 && resolve();
            }
            console.log(3)
        }).then(function(){
            console.log(4)
        })
        console.log(5)

• 输出23541

setTimeout(function(){
            console.log(1)
        }, 0);
        new Promise(function excutor(resolve) {
            console.log(2);
            setTimeout(function(){
            resolve()
        }, 0);
            console.log(3)
        }).then(function(){
            console.log(4)
        })
        console.log(5)

• 输出23514
• 总结：then的回调函数会在当前脚本同步任务执行完后执行，但setTimeout会将回调函数添加到任务的末尾，即resolve延迟到同步的末尾

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