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What is the meaning of identifiers in javascript

青灯夜游
青灯夜游Original
2021-06-15 17:41:584306browse

在javascript中,标识符是指用户编程时使用的名字,用于给变量、常量、函数、语句块等命名,以建立起名称与使用之间的关系;标识符通常由字母和数字以及其它字符构成。合法的标识符其第一个字符必须是字母、下划线或美元符号;且不能与JavaScript关键字、保留字重名。

What is the meaning of identifiers in javascript

本教程操作环境:windows7系统、javascript1.8.5版、Dell G3电脑

javascript标识符

标识符(Identifier)就是名称的专业术语。JavaScript 标识符包括变量名、函数名、参数名和属性名。

标识符是用户编程时使用的名字,用于给变量、常量、函数、语句块等命名,以建立起名称与使用之间的关系。标识符通常由字母和数字以及其它字符构成。

合法的标识符应该注意以下强制规则:

  • 第一个字符必须是字母、下划线(_)或美元符号($)。

    What is the meaning of identifiers in javascript

  • 除了第一个字符外,其他位置可以使用 Unicode 字符。一般建议仅使用 ASCII 编码的字母,不建议使用双字节的字符。

  • 不能与 JavaScript 关键字、保留字重名。

    What is the meaning of identifiers in javascript

    What is the meaning of identifiers in javascript

  • 可以使用 Unicode 转义序列。例如,字符 a 可以使用“\u0061”表示。

示例

在下面示例中,定义变量 a,使用 Unicode 转义序列表示变量名。

var \u0061 = "字符 a 的 Unicode 转义序列是 \\0061";
document.write(\u0061);

使用转义序列不是很方便,一般常用转义序列表示特殊字符或名称,如 JavaScript 关键字、程序脚本等。

关键字

关键字就是 ECMA-262 规定的 JavaScript 语言内部使用的一组名称(或称为命令)。这些名称具有特定的用途,用户不能自定义同名的标识符。具体说明如表所示。

ECMAScript 关键字
break delete  if this  while
case do in throw with
catch  else  instanceof  try  
continue  finally  new  typeof  
debugger(ECMAScript 5 新增) for  return  var  
default  function  switch  void  

Reserved words

Reserved words are a set of names (or commands) prepared for use within the JavaScript language specified by ECMA-262. These names currently have no specific purpose and are reserved for JavaScript upgrade versions. Users are advised not to use them. Specific instructions are shown in the table.

ECMAScript reserved words
abstract double goto native static
boolean enum implements package super
byte export import private synchronized
char extends int protected throws
class final interface public transient
const float long short volatile

ECMAScript 3 lists all Java keywords as reserved words, while ECMAScript 5 has more flexible regulations.

For example, in non-strict mode, only class, const, enums, export, extends, import, and super are reserved words, and other ECMAScript 3 reserved words can be used freely; in strict mode, ECMAScript 5 becomes Be more cautious and strictly limit the use of implements, interface, let, package, private, protected, public, static, yield, eval (non-reserved words), and arguments (non-reserved words).

JavaScript predefines many global variables and functions, and users should avoid using them. Specific instructions are shown in the table.

##Array encodeURLComponent isFinite Object StringBoolean Error isNaN parseFloat SyntaxErrorDate eval JSON parseInt TypeErrordecodeURL EvalError Math RangeError undefined##decodeURLComponent [Related recommendations:
JavaScript predefined global variables and functions
arguments encodeURL Infinity Number RegExp
Function NaN ReferenceError URLError
javascript learning tutorial

]

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