promise 笔记

拒绝：

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

            throw new Error(0);

        });

        promise.then(function(arg){

            console.log(arg);

        }).catch(function(arg){

            console.log('c' + arg);//走这

        });

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

            reject(0);

        });

        promise.then(function(arg){

            console.log(arg);

        },function(arg){

            console.log('j' + arg);//走这

        }).catch(function(arg){

            console.log('c' + arg);

异常：

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

            throw new Error(0);

        });

        promise.then(function(arg){

            console.log(arg);

        }).catch(function(arg){

            console.log('c' + arg);//走这

        });

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

            reject(0);

        });

        promise.then(function(arg){

            console.log(arg);

        },function(arg){

            console.log('j' + arg);//走这

        }).catch(function(arg){

            console.log('c' + arg);

then() cath()会构建和返回一个promise实例：

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

            throw new Error('x');

        });

        promise.then(function(arg){

            console.log(arg);

            return 'xx';//返回给下一个then的resolve（抛异常也是下一个then的resolve）

        },function(arg){

            console.log('reject：' + arg);

            return 'xx';//返回给下一个then的reject

        }).catch(function(arg){

            console.log('cathc' + arg);

        })

        .then(function(data){

            console.log('last resolve:' + data);

        },function(data){

            console.log('last reject:' + data);

        });

延迟，异步异常

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

            setTimeout(function() {

                reject('x');//能够捕获，若是是 throw 一个error就没法捕获

            });

        });

        promise.then(function(arg) {

                console.log('resole:' + arg);

            }, function(arg) {

                console.log('reject：' + arg);

            })

            .catch(function(arg) {

                console.log('cathc:' + arg);

            })

补充：

window.addEventListener("unhandledrejection", function (event) {

  console.warn("WARNING: Unhandled promise rejection. Shame on you! Reason: "

               + event.reason);});

用来捕获拒绝，window.onerror只是捕获异常不会捕获promise的拒绝