JavaScript 语法5757

JavaScript 语法

JavaScript 是一个程序语言。语法规则定义了语言结构。

JavaScript 语法

JavaScript 是一个脚本语言。

它是一个轻量级，但功能强大的编程语言。

JavaScript 字面量

在编程语言中，一般固定值称为字面量，如 3.14。

数字（Number）字面量 可以是整数或者是小数，或者是科学计数(e)。

3.14 1001 123e5

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字符串（String）字面量 可以使用单引号或双引号:

"John Doe" 'John Doe'

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表达式字面量 用于计算：

5 + 6 5 * 10

尝试一下 »

数组（Array）字面量 定义一个数组：

[40, 100, 1, 5, 25, 10]

对象（Object）字面量 定义一个对象：

{firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"}

函数（Function）字面量 定义一个函数：

function myFunction(a, b) { return a * b;}

JavaScript 变量

在编程语言中，变量用于存储数据值。

JavaScript 使用关键字 var 来定义变量， 使用等号来为变量赋值：

var x, length x = 5 length = 6

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变量可以通过变量名访问。在指令式语言中，变量通常是可变的。字面量是一个恒定的值。

JavaScript 操作符

JavaScript使用 算术运算符 来计算值:

(5 + 6) * 10

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JavaScript使用赋值运算符给变量赋值：

x = 5 y = 6 z = (x + y) * 10

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JavaScript语言有多种类型的运算符：

JavaScript 语句

在 HTML 中，JavaScript 语句用于向浏览器发出命令。

语句是用分号分隔：

x = 5 + 6; y = x * 10;

JavaScript 关键字

JavaScript 关键字用于标识要执行的操作。

和其他任何编程语言一样，JavaScript 保留了一些关键字为自己所用。

var 关键字告诉浏览器创建一个新的变量：

var x = 5 + 6; var y = x * 10;

JavaScript 同样保留了一些关键字，这些关键字在当前的语言版本中并没有使用，但在以后 JavaScript 扩展中会用到。

以下是 JavaScript 中最​​重要的保留关键字（按字母顺序）：