为什么我应该在 javascript 中的每个函数后使用分号?

问题描述

我见过不同的开发人员在 javascript 中的函数后包含分号，有些则没有.哪个是最佳做法?

I've seen different developers include semicolons after functions in javascript and some haven't. Which is best practice?

function weLikeSemiColons(arg) {
   // bunch of code
};

或

function unnecessary(arg) {
  // bunch of code
}

推荐答案

函数声明后的分号不需要.

FunctionDeclaration 的语法在 规范 如下:

function Identifier ( FormalParameterListopt ) { FunctionBody }

语法上不需要分号，但可能想知道为什么?

There's no semicolon grammatically required, but might wonder why?

分号用于将语句彼此分开，并且FunctionDeclaration不是语句.

Semicolons serve to separate statements from each other, and a FunctionDeclaration is not a statement.

FunctionDeclarations 被评估在代码进入执行之前，提升是用于解释这种行为的常用词.

FunctionDeclarations are evaluated before the code enters into execution, hoisting is a common word used to explain this behaviour.

术语函数声明"和函数语句"经常被错误地互换使用，因为 ECMAScript 规范中没有描述函数语句，但是有一些实现在其语法中包含函数语句，尤其是 Mozilla-但这又是非标准的.

The terms "function declaration" and "function statement" are often wrongly used interchangeably, because there is no function statement described in the ECMAScript Specification, however there are some implementations that include a function statement in their grammar, -notably Mozilla- but again this is non-standard.

然而，在使用 FunctionExpressions 的地方总是推荐使用分号，例如:

However semicolons are always recommended where you use FunctionExpressions, for example:

var myFn = function () {
  //...
};

(function () {
  //...
})();

如果在上面的例子中省略第一个函数后面的分号，你会得到完全不想要的结果:

If you omit the semicolon after the first function in the above example, you will get completely undesired results:

var myFn = function () {
  alert("Surprise!");
} // <-- No semicolon!

(function () {
  //...
})();

第一个函数将立即执行，因为第二个函数周围的括号将被解释为函数调用的Arguments.

The first function will be executed immediately, because the parentheses surrounding the second one, will be interpreted as the Arguments of a function call.

推荐讲座:

• 命名函数表达式揭秘(好文章)
• 解释 JavaScript 的封装匿名函数语法(更多关于 FunctionDeclaration vs FunctionExpression)

• Named function expressions demystified (great article)
• Explain JavaScript’s encapsulated anonymous function syntax (more on FunctionDeclaration vs FunctionExpression)

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