From 6b300cf4911eefb2b2d2b98f150a2d2269697ba8 Mon Sep 17 00:00:00 2001 From: waiting <1661926154@qq.com> Date: Wed, 8 Nov 2017 17:38:17 +0800 Subject: [PATCH 1/3] Use const instead of var --- docs/promise.md | 56 ++++++++++++++++++++++++------------------------- 1 file changed, 28 insertions(+), 28 deletions(-) diff --git a/docs/promise.md b/docs/promise.md index bd80090..7ea9e42 100644 --- a/docs/promise.md +++ b/docs/promise.md @@ -27,7 +27,7 @@ ES6 规定，`Promise`对象是一个构造函数，用来生成`Promise`实例 下面代码创造了一个`Promise`实例。 ```javascript -var promise = new Promise(function(resolve, reject) { +const promise = new Promise(function(resolve, reject) { // ... some code if (/* 异步操作成功 */){ @@ -96,7 +96,7 @@ console.log('Hi!'); ```javascript function loadImageAsync(url) { return new Promise(function(resolve, reject) { - var image = new Image(); + const image = new Image(); image.onload = function() { resolve(image); @@ -116,9 +116,9 @@ function loadImageAsync(url) { 下面是一个用`Promise`对象实现的 Ajax 操作的例子。 ```javascript -var getJSON = function(url) { - var promise = new Promise(function(resolve, reject){ - var client = new XMLHttpRequest(); +const getJSON = function(url) { + const promise = new Promise(function(resolve, reject){ + const client = new XMLHttpRequest(); client.open("GET", url); client.onreadystatechange = handler; client.responseType = "json"; @@ -152,11 +152,11 @@ getJSON("/posts.json").then(function(json) { 如果调用`resolve`函数和`reject`函数时带有参数，那么它们的参数会被传递给回调函数。`reject`函数的参数通常是`Error`对象的实例，表示抛出的错误；`resolve`函数的参数除了正常的值以外，还可能是另一个 Promise 实例，比如像下面这样。 ```javascript -var p1 = new Promise(function (resolve, reject) { +const p1 = new Promise(function (resolve, reject) { // ... }); -var p2 = new Promise(function (resolve, reject) { +const p2 = new Promise(function (resolve, reject) { // ... resolve(p1); }) @@ -167,11 +167,11 @@ var p2 = new Promise(function (resolve, reject) { 注意，这时`p1`的状态就会传递给`p2`，也就是说，`p1`的状态决定了`p2`的状态。如果`p1`的状态是`pending`，那么`p2`的回调函数就会等待`p1`的状态改变；如果`p1`的状态已经是`resolved`或者`rejected`，那么`p2`的回调函数将会立刻执行。 ```javascript -var p1 = new Promise(function (resolve, reject) { +const p1 = new Promise(function (resolve, reject) { setTimeout(() => reject(new Error('fail')), 3000) }) -var p2 = new Promise(function (resolve, reject) { +const p2 = new Promise(function (resolve, reject) { setTimeout(() => resolve(p1), 1000) }) @@ -276,7 +276,7 @@ p.then((val) => console.log('fulfilled:', val)) 下面是一个例子。 ```javascript -var promise = new Promise(function(resolve, reject) { +const promise = new Promise(function(resolve, reject) { throw new Error('test'); }); promise.catch(function(error) { @@ -289,7 +289,7 @@ promise.catch(function(error) { ```javascript // 写法一 -var promise = new Promise(function(resolve, reject) { +const promise = new Promise(function(resolve, reject) { try { throw new Error('test'); } catch(e) { @@ -301,7 +301,7 @@ promise.catch(function(error) { }); // 写法二 -var promise = new Promise(function(resolve, reject) { +const promise = new Promise(function(resolve, reject) { reject(new Error('test')); }); promise.catch(function(error) { @@ -314,7 +314,7 @@ promise.catch(function(error) { 如果Promise状态已经变成`resolved`，再抛出错误是无效的。 ```javascript -var promise = new Promise(function(resolve, reject) { +const promise = new Promise(function(resolve, reject) { resolve('ok'); throw new Error('test'); }); @@ -399,7 +399,7 @@ process.on('unhandledRejection', function (err, p) { 再看下面的例子。 ```javascript -var promise = new Promise(function (resolve, reject) { +const promise = new Promise(function (resolve, reject) { resolve('ok'); setTimeout(function () { throw new Error('test') }, 0) }); @@ -413,7 +413,7 @@ promise.then(function (value) { console.log(value) }); 一般总是建议，Promise 对象后面要跟`catch`方法，这样可以处理 Promise 内部发生的错误。`catch`方法返回的还是一个 Promise 对象，因此后面还可以接着调用`then`方法。 ```javascript -var someAsyncThing = function() { +const someAsyncThing = function() { return new Promise(function(resolve, reject) { // 下面一行会报错，因为x没有声明 resolve(x + 2); @@ -449,7 +449,7 @@ Promise.resolve() `catch`方法之中，还能再抛出错误。 ```javascript -var someAsyncThing = function() { +const someAsyncThing = function() { return new Promise(function(resolve, reject) { // 下面一行会报错，因为x没有声明 resolve(x + 2); @@ -491,7 +491,7 @@ someAsyncThing().then(function() { `Promise.all`方法用于将多个 Promise 实例，包装成一个新的 Promise 实例。 ```javascript -var p = Promise.all([p1, p2, p3]); +const p = Promise.all([p1, p2, p3]); ``` 上面代码中，`Promise.all`方法接受一个数组作为参数，`p1`、`p2`、`p3`都是 Promise 实例，如果不是，就会先调用下面讲到的`Promise.resolve`方法，将参数转为 Promise 实例，再进一步处理。（`Promise.all`方法的参数可以不是数组，但必须具有 Iterator 接口，且返回的每个成员都是 Promise 实例。） @@ -506,7 +506,7 @@ var p = Promise.all([p1, p2, p3]); ```javascript // 生成一个Promise对象的数组 -var promises = [2, 3, 5, 7, 11, 13].map(function (id) { +const promises = [2, 3, 5, 7, 11, 13].map(function (id) { return getJSON('/post/' + id + ".json"); }); @@ -586,7 +586,7 @@ Promise.all([p1, p2]) `Promise.race`方法同样是将多个Promise实例，包装成一个新的Promise实例。 ```javascript -var p = Promise.race([p1, p2, p3]); +const p = Promise.race([p1, p2, p3]); ``` 上面代码中，只要`p1`、`p2`、`p3`之中有一个实例率先改变状态，`p`的状态就跟着改变。那个率先改变的 Promise 实例的返回值，就传递给`p`的回调函数。 @@ -613,7 +613,7 @@ p.catch(error => console.log(error)); 有时需要将现有对象转为Promise对象，`Promise.resolve`方法就起到这个作用。 ```javascript -var jsPromise = Promise.resolve($.ajax('/whatever.json')); +const jsPromise = Promise.resolve($.ajax('/whatever.json')); ``` 上面代码将jQuery生成的`deferred`对象，转为一个新的Promise对象。 @@ -666,7 +666,7 @@ p1.then(function(value) { 如果参数是一个原始值，或者是一个不具有`then`方法的对象，则`Promise.resolve`方法返回一个新的Promise对象，状态为`resolved`。 ```javascript -var p = Promise.resolve('Hello'); +const p = Promise.resolve('Hello'); p.then(function (s){ console.log(s) @@ -683,7 +683,7 @@ p.then(function (s){ 所以，如果希望得到一个Promise对象，比较方便的方法就是直接调用`Promise.resolve`方法。 ```javascript -var p = Promise.resolve(); +const p = Promise.resolve(); p.then(function () { // ... @@ -717,9 +717,9 @@ console.log('one'); `Promise.reject(reason)`方法也会返回一个新的 Promise 实例，该实例的状态为`rejected`。 ```javascript -var p = Promise.reject('出错了'); +const p = Promise.reject('出错了'); // 等同于 -var p = new Promise((resolve, reject) => reject('出错了')) +const p = new Promise((resolve, reject) => reject('出错了')) p.then(null, function (s) { console.log(s) @@ -814,7 +814,7 @@ Promise.prototype.finally = function (callback) { ```javascript const preloadImage = function (path) { return new Promise(function (resolve, reject) { - var image = new Image(); + const image = new Image(); image.onload = resolve; image.onerror = reject; image.src = path; @@ -833,9 +833,9 @@ function getFoo () { }); } -var g = function* () { +const g = function* () { try { - var foo = yield getFoo(); + const foo = yield getFoo(); console.log(foo); } catch (e) { console.log(e); @@ -843,7 +843,7 @@ var g = function* () { }; function run (generator) { - var it = generator(); + const it = generator(); function go(result) { if (result.done) return result.value; From 08a623935ecc7bb35f1419a40c3f2eff98fac1de Mon Sep 17 00:00:00 2001 From: waiting <1661926154@qq.com> Date: Wed, 8 Nov 2017 17:41:35 +0800 Subject: [PATCH 2/3] Use function assign instead of function declaration inner function MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 在函数内定义函数推荐使用变量赋值方式代替函数声明方式 --- docs/promise.md | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) diff --git a/docs/promise.md b/docs/promise.md index 7ea9e42..78ae462 100644 --- a/docs/promise.md +++ b/docs/promise.md @@ -118,14 +118,7 @@ function loadImageAsync(url) { ```javascript const getJSON = function(url) { const promise = new Promise(function(resolve, reject){ - const client = new XMLHttpRequest(); - client.open("GET", url); - client.onreadystatechange = handler; - client.responseType = "json"; - client.setRequestHeader("Accept", "application/json"); - client.send(); - - function handler() { + const handler = function () { if (this.readyState !== 4) { return; } @@ -135,6 +128,13 @@ const getJSON = function(url) { reject(new Error(this.statusText)); } }; + const client = new XMLHttpRequest(); + client.open("GET", url); + client.onreadystatechange = handler; + client.responseType = "json"; + client.setRequestHeader("Accept", "application/json"); + client.send(); + }); return promise; From 5c40c2be8dc705571fe8f80b792b218cb2bd1b33 Mon Sep 17 00:00:00 2001 From: waiting <1661926154@qq.com> Date: Wed, 8 Nov 2017 19:19:40 +0800 Subject: [PATCH 3/3] Format style --- docs/promise.md | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/docs/promise.md b/docs/promise.md index 78ae462..8b8c0fc 100644 --- a/docs/promise.md +++ b/docs/promise.md @@ -118,7 +118,7 @@ function loadImageAsync(url) { ```javascript const getJSON = function(url) { const promise = new Promise(function(resolve, reject){ - const handler = function () { + const handler = function() { if (this.readyState !== 4) { return; }