diff --git a/1-js/02-first-steps/16-javascript-specials/article.md b/1-js/02-first-steps/16-javascript-specials/article.md index 44dd8e3e1c..b163a40106 100644 --- a/1-js/02-first-steps/16-javascript-specials/article.md +++ b/1-js/02-first-steps/16-javascript-specials/article.md @@ -1,23 +1,23 @@ -# JavaScript specials +# JavasScript 特性 -This chapter briefly recaps the features of JavaScript that we've learned by now, paying special attention to subtle moments. +本章简要回顾我们到现在为止学到的 JavaScript 特性，特别注意一些细节。 -## Code structure +## 代码结构 -Statements are delimited with a semicolon: +语句用分号分隔： ```js run no-beautify alert('Hello'); alert('World'); ``` -Usually, a line-break is also treated as a delimiter, so that would also work: +通常，换行符也被视为分隔符： ```js run no-beautify alert('Hello') alert('World') ``` -That's called "automatic semicolon insertion". Sometimes it doesn't work, for instance: +这就是所谓的「自动分号插入」。有时它不起作用，例如： ```js run alert("There will be an error after this message") @@ -25,27 +25,27 @@ alert("There will be an error after this message") [1, 2].forEach(alert) ``` -Most codestyle guides agree that we should put a semicolon after each statement. +大多数代码风格指南都认为我们应该在每个语句后面加上分号。 -Semicolons are not required after code blocks `{...}` and syntax constructs with them like loops: +在代码块 `{...}` 之后以及循环语句后不需要使用分号： ```js function f() { - // no semicolon needed after function declaration + //函数声明后不需要分号 } for(;;) { - // no semicolon needed after the loop +  //循环语句后不需要分号 } -``` -...But even if we can put an "extra" semicolon somewhere, that's not an error. It will be ignored. +``` -More in: . +...但即使我们可以在某处添加了「额外」分号，这也不是错误。它会被忽略的。 +更多信息：。 -## Strict mode +## 严格模式 -To fully enable all features of modern JavaScript, we should start scripts with `"use strict"`. +为了完全启用现代 JavaScript 的所有功能，我们应该使用 `"use strict"` 指令。 ```js 'use strict'; @@ -53,67 +53,68 @@ To fully enable all features of modern JavaScript, we should start scripts with ... ``` -The directive must be at the top of a script or at the beginning of a function. +该指令必须位于 JavaScript 文件的顶部或函数的开头。 -Without `"use strict"`, everything still works, but some features behave in the old-fashion, "compatible" way. We'd generally prefer the modern behavior. +如果没有使用严格模式，所有东西仍可以正常工作，但是某些特性的表现方式与旧式「兼容」方式相同。我们通常喜欢更现代的方式。 -Some modern features of the language (like classes that we'll study in the future) enable strict mode implicitly. +语言的一些现代特征（比如我们将来要学习的类）会隐式地启用严格模式。 -More in: . +更多信息：。 -## Variables +## 变量 -Can be declared using: +可以使用以下方式声明变量： - `let` -- `const` (constant, can't be changed) -- `var` (old-style, will see later) +- `const` (固定的，不能被改变) +- `var`（旧式的，稍后会看到） -A variable name can include: -- Letters and digits, but the first character may not be a digit. -- Characters `$` and `_` are normal, on par with letters. -- Non-Latin alphabets and hieroglyphs are also allowed, but commonly not used. +一个合格的变量名可以由以下组成： +- 字符串和数字，但是第一个字符不能是数字。 +- 字符 `$` 和 `_` 是允许的，用法同字母。 +- 非拉丁字母和象形文字也是允许的，但通常不会使用。 -Variables are dynamically typed. They can store any value: + +变量的值可以动态改变数据类型，它们可以存储任何价： ```js let x = 5; x = "John"; ``` -There are 7 data types: +有 7 种数据类型： + +- `number` —— 可以是浮点数，也可以是整数， +- `string` —— 字符串类型， +- `boolean` —— 逻辑值: `true/false`， +- `null` —— 具有单个值 `null` 的类型，表示”空“或“不存在”， +- `undefined` —— 一个具有单个值 `undefined` 的类型，表示「未分配」， +- `object` 和 `symbol` —— 对于复杂的数据结构和唯一标识符，我们目前还没学习这个类型。 -- `number` for both floating-point and integer numbers, -- `string` for strings, -- `boolean` for logical values: `true/false`, -- `null` -- a type with a single value `null`, meaning "empty" or "does not exist", -- `undefined` -- a type with a single value `undefined`, meaning "not assigned", -- `object` and `symbol` -- for complex data structures and unique identifiers, we haven't learnt them yet. +`typeof` 运算符返回值的类型，但有两个例外： -The `typeof` operator returns the type for a value, with two exceptions: ```js typeof null == "object" // error in the language -typeof function(){} == "function" // functions are treated specially +typeof function(){} == "function" // 函数特殊 ``` -More in: and . +更多信息： 和 。 -## Interaction - -We're using a browser as a working environment, so basic UI functions will be: +## 交互 +我们使用浏览器作为工作环境，所以基本的 UI 功能将是： [`prompt(question[, default])`](mdn:api/Window/prompt) -: Ask a `question`, and return either what the visitor entered or `null` if he pressed "cancel". +: 询问一个问题，并返回访问者输入的内容，如果他按下「取消」则返回 `null`。 [`confirm(question)`](mdn:api/Window/confirm) -: Ask a `question` and suggest to choose between Ok and Cancel. The choice is returned as `true/false`. +: 提出一个问题，并建议在确定和取消之间进行选择。该选项以 `true/false` 形式返回。 [`alert(message)`](mdn:api/Window/alert) -: Output a `message`. +: 输出一个 `消息`。 -All these functions are *modal*, they pause the code execution and prevent the visitor from interacting with the page until he answers. +所有这些函数都会产生**模态框**，它们会暂停代码执行并阻止访问者与页面交互，直到用户输入内容。 -For instance: +举个例子： ```js run let userName = prompt("Your name?", "Alice"); @@ -123,58 +124,55 @@ alert( "Visitor: " + userName ); // Alice alert( "Tea wanted: " + isTeaWanted ); // true ``` -More in: . - -## Operators +更多信息：。 -JavaScript supports the following operators: +## 运算符 -Arithmetical -: Regular: `* + - /`, also `%` for the remainder and `**` for power of a number. +JavaScript 支持以下运算符： - The binary plus `+` concatenates strings. And if any of the operands is a string, the other one is converted to string too: +算数运算符 +: 常规的比如：`+ - * /`（加减乘除），以及取余操作 `%` 和幂运算符 `**` 。 + 二进制加 `+` 连接字符串。如果任何一个操作数是一个字符串，另一个操作数也将转换为字符串： ```js run - alert( '1' + 2 ); // '12', string - alert( 1 + '2' ); // '12', string + alert( '1' + 2 ); // '12', 字符串 + alert( 1 + '2' ); // '12', 字符串 ``` -Assignments -: There is a simple assignment: `a = b` and combined ones like `a *= 2`. +赋值 +: 简单的赋值：`a = b` 和连续赋值：`a * = 2`。 -Bitwise -: Bitwise operators work with integers on bit-level: see the [docs](mdn:/JavaScript/Reference/Operators/Bitwise_Operators) when they are needed. +按位操作 +: 位运算符在位级上使用整数：当需要时，请参阅 [docs](mdn:/JavaScript/Reference/Operators/Bitwise_Operators)。 -Ternary -: The only operator with three parameters: `cond ? resultA : resultB`. If `cond` is truthy, returns `resultA`, otherwise `resultB`. +三元运算 +: 唯一具有三个参数的操作：`cond？ resultA: resultB`。如果 `cond` 是真的，则返回 `resultA`，否则返回 `resultB`。 -Logical operators -: Logical AND `&&` and OR `||` perform short-circuit evaluation and then return the value where it stopped. +逻辑运算符 +: 逻辑与 `&&` 和或 `||` 执行短路评估，然后返回停止时的值。 -Comparisons -: Equality check `==` for values of different types converts them to a number (except `null` and `undefined` that equal each other and nothing else), so these are equal: +比较运算符 +: 运算符 `==` 将不同类型的值转换为一个数字（除了 `null` 和 `undefined`，它们彼此相等而没有别的情况），所以下面的例子是相等的： ```js run alert( 0 == false ); // true alert( 0 == '' ); // true ``` + 其他比较也转换为数字。 - Other comparisons convert to a number as well. - - The strict equality operator `===` doesn't do the conversion: different types always mean different values for it, so: + 严格相等运算符 `===` 不会进行转换：不同的类型总是为其指定不同的值，因此： + 值 `null` 和 `undefined` 是特殊的：它们只在 `==` 下相等。 + 字符串按照字符顺序逐一比较，其他类型转换为数字。 - Values `null` and `undefined` are special: they equal `==` each other and don't equal anything else. - - Greater/less comparisons compare strings character-by-character, other types are converted to a number. - -Logical operators -: There are few others, like a comma operator. +逻辑运算符 +: 其他合规的运算符比较少，其中有逗号运算符。 More in: , , . +更多信息：, , 。 -## Loops +## 循环语句 -- We covered 3 types of loops: +- 我们涵盖了 3 种类型的循环： ```js // 1 @@ -193,26 +191,25 @@ More in: , , . } ``` -- The variable declared in `for(let...)` loop is visible only inside the loop. But we can also omit `let` and reuse an existing variable. -- Directives `break/continue` allow to exit the whole loop/current iteration. Use labels to break nested loops. +- 在 `for(let...)` 循环中声明的变量只在循环中可见。但是我们也可以省略 `let` 并重用现有的变量。 +- 指令 `break/continue` 允许退出整个循环/当前迭代。使用标签来打破嵌套循环。 -Details in: . +详情参见：。 -Later we'll study more types of loops to deal with objects. +稍后我们将学习更多类型的循环语句来处理事物。 -## The "switch" construct +## "switch" 结构 -The "switch" construct can replace multiple `if` checks. It uses `===` (strict equality) for comparisons. +"switch" 结构可以替代多个 `if` 检查，它内部使用 `===`（严格相等）进行比较。 -For instance: +例如： ```js run let age = prompt('Your age?', 18); switch (age) { case 18: - alert("Won't work"); // the result of prompt is a string, not a number - + alert("Won't work"); //提示的结果是一个字符串，而不是数字 case "18": alert("This works!"); break; @@ -222,13 +219,13 @@ switch (age) { } ``` -Details in: . +详情参见：。 -## Functions +## 函数 -We covered three ways to create a function in JavaScript: +我们介绍了三种在 JavaScript 中创建函数的方法： -1. Function Declaration: the function in the main code flow +1. 函数声明：主代码流中的函数 ```js function sum(a, b) { @@ -238,7 +235,7 @@ We covered three ways to create a function in JavaScript: } ``` -2. Function Expression: the function in the context of an expression +2. 函数表达式：表达式上下文中的函数 ```js let sum = function(a, b) { @@ -247,41 +244,38 @@ We covered three ways to create a function in JavaScript: return result; } ``` + 函数表达式可以有一个名字，比如 `sum = function name（a，b）`，但是 `name` 只在该函数内可见。 - Function expressions can have a name, like `sum = function name(a, b)`, but that `name` is only visible inside that function. - -3. Arrow functions: +3. 箭头函数： ```js - // expression at the right side + //表达式在右侧 let sum = (a, b) => a + b; - // or multi-line syntax with { ... }, need return here: + // 或带{...}的多行语法，需要此处返回： let sum = (a, b) => { // ... return a + b; } - // without arguments + //没有参数 let sayHi = () => alert("Hello"); - // with a single argument + //有一个参数 let double = n => n * 2; ``` +- 函数可能具有局部变量：在其内部声明的变量。这些变量只在函数内部可见。 +- 参数可以有默认值：`function sum(a = 1, b = 2) {...}`。 +- 函数总是返回一些东西。如果没有 `return` 语句，那么结果是 `undefined`。 -- Functions may have local variables: those declared inside its body. Such variables are only visible inside the function. -- Parameters can have default values: `function sum(a = 1, b = 2) {...}`. -- Functions always return something. If there's no `return` statement, then the result is `undefined`. - - -| Function Declaration | Function Expression | +|函数声明|函数表达式| |----------------------|---------------------| -| visible in the whole code block | created when the execution reaches it | -| - | can have a name, visible only inside the function | +|在整个代码块中可见|在执行到达时创建| +| - |可以有一个名字，只在函数内部可见| -More: see , . +更多：参见，。 -## More to come +## 更多 -That was a brief list of JavaScript features. As of now we've studied only basics. Further in the tutorial you'll find more specials and advanced features of JavaScript. +这是 JavaScript 功能的简要概述。截至目前，我们只研究基础知识。随着教程的深入，您会发现更多特殊功能和 JavaScript 高级功能。