js 风格(注意事项)
类型
• 原始类型:我们可以直接使用值。
ο string
ο number
ο boolean
ο null
ο undefined
var foo = 1, bar = foo; bar = 9; console.log(foo, bar); // => 1, 9
• 复合类型:我们通过`引用`对值进行间接访问。
ο object
ο array
ο function
var foo = [1, 2], bar = foo; bar[0] = 9; console.log(foo[0], bar[0]); // => 9, 9
Objects
• 使用{}创建对象。
// bad var item = new Object(); // good var item = {};
• 不要使用保留字作为关键字。
// bad var superman = { class: 'superhero', default: { clark: 'kent' }, private: true }; // good var superman = { klass: 'superhero', defaults: { clark: 'kent' }, hidden: true };
Arrays
// bad var items = new Array(); // good var items = [];
• 如果你不知道数组长度,使用Array#push。
var someStack = []; // bad someStack[someStack.length] = 'abracadabra'; // good someStack.push('abracadabra');
• 当你需要复制数组的时候,请使用Array#slice。
var len = items.length, itemsCopy = [], i; // bad for (i = 0; i < len; i++) { itemsCopy[i] = items[i]; } // good itemsCopy = items.slice();
Strings
• 对于字符串,我们使用单引号''。
// bad var name = "Bob Parr"; // good var name = 'Bob Parr'; // bad var fullName = "Bob " + this.lastName; // good var fullName = 'Bob ' + this.lastName;
• 超过80个字符的字符串,我们使用串联符号(\),让字符串多行显示。
• 注意:如果过度使用带串联符号的字符可能会影响到性能。
// bad var errorMessage = 'This is a super long error that was thrown because of Batman. When you stop to think about how Batman had anything to do with this, you would get nowhere fast.'; // bad var errorMessage = 'This is a super long error that \ was thrown because of Batman. \ When you stop to think about \ how Batman had anything to do \ with this, you would get nowhere \ fast.'; // good var errorMessage = 'This is a super long error that ' + 'was thrown because of Batman.' + 'When you stop to think about ' + 'how Batman had anything to do ' + 'with this, you would get nowhere ' + 'fast.';
• 当我们在编程的时候,需要拼接出一个字符串,我们可以使用Array#join 代替字符串连接。尤其是对IE浏览器。
var items, messages, length, i; messages = [{ state: 'success', message: 'This one worked.' },{ state: 'success', message: 'This one worked as well.' },{ state: 'error', message: 'This one did not work.' }]; length = messages.length; // bad function inbox(messages) { items = '<ul>'; for (i = 0; i < length; i++) { items += '<li>' + messages[i].message + '</li>'; } return items + '</ul>'; } // good function inbox(messages) { items = []; for (i = 0; i < length; i++) { items[i] = messages[i].message; } return '<ul><li>' + items.join('</li><li>') + '</li></ul>'; }
Functions
• 函数表达式
// anonymous function expression var anonymous = function() { return true; }; // named function expression var named = function named() { return true; }; // immediately-invoked function expression (IIFE) (function() { console.log('Welcome to the Internet. Please follow me.'); })();
• 绝对不要在非函数块(if,while)申明一个函数。我们可以把函数申明变成一个函数表达式。
// bad if (currentUser) { function test() { console.log('Nope.'); } } // good if (currentUser) { var test = function test() { console.log('Yup.'); }; }
• 绝对不要把一个参数命名为arguments,arguments参数是函数作用域内给出的一个特殊变量,如果你把参数命名为arguments,那么这个参数就会覆盖它原有的特殊变量。
// bad function nope(name, options, arguments) { // ...stuff... } // good function yup(name, options, args) { // ...stuff... }