es6之promise

let ajax=function(){
        console.log("执行");
        return new Promise(function(resolve,reject){
            setTimeout(function(){
                resolve()
            },1000)
        })
    }
    ajax().then(function(){
        console.log("promise","timeout");
    })

let ajax=function(){
        console.log("执行1");
        return new Promise(function(resolve,reject){
            setTimeout(function(){
                resolve()
            },1000)
        })
    }
    ajax()
        .then(function(){
        return new Promise(function(resolve,reject){
            setTimeout(function(){
                resolve()
            },2000)
        })
        .then(function(){
            console.log("timeout3")
        })

    })

let ajax=function(num){
        console.log("执行乐乐乐");
        return new Promise(function(resolve,reject){
            if(num>5){
                resolve()
            }else{
                throw Error("出错了");
            }
        })
    }
    ajax(6).then(function(){
        console.log("执行第二步");
    }).catch(function(err){
        console.log("catch",err);
    })
    ajax(1).then(function(){
        console.log("执行第二步");
    }).catch(function(err){
        console.log("catch",err);
    })