promise 筆記

拒絕：

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);//走這

        });

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

            reject(0);

        });

        promise.then(function(arg){

            console.log(arg);

        },function(arg){

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

        }).catch(function(arg){

            console.log('c' + arg);

異常：

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);//走這

        });

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

            reject(0);

        });

        promise.then(function(arg){

            console.log(arg);

        },function(arg){

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

        }).catch(function(arg){

            console.log('c' + arg);

then() cath()會構建和返回一個promise實例：

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

            throw new Error('x');

        });

        promise.then(function(arg){

            console.log(arg);

            return 'xx';//返回給下一個then的resolve（拋異常也是下一個then的resolve）

        },function(arg){

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

            return 'xx';//返回給下一個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);

        });

延遲，異步異常

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

            setTimeout(function() {

                reject('x');//能夠捕獲，若是是 throw 一個error就沒法捕獲

            });

        });

        promise.then(function(arg) {

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

            }, function(arg) {

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

            })

            .catch(function(arg) {

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

            })

補充：

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

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

               + event.reason);});

用來捕獲拒絕，window.onerror只是捕獲異常不會捕獲promise的拒絕