为什么我应该在javascript中的每个函数后使用分号？ [英] Why should I use a semicolon after every function in javascript?

问题描述

我见过不同的开发人员在javascript函数之后包含分号，而有些则没有。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 不必。

规范中描述了 FunctionDeclaration 的语法如下：

The grammar of a FunctionDeclaration is described in the specification as this:

function Identifier ( FormalParameterListopt ) { FunctionBody }

语法上没有分号，但可能想知道为什么？

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

分号用于分隔声明彼此， FunctionDeclaration 不是声明。

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

FunctionDeclarations 被评估 hoisting 是一个常用词，用于解释这种行为。

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声明经常被错误地互换使用，因为ECMAScript规范中没有描述函数声明，但是有一些实现包含函数声明在他们的语法中， - 特别是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.

但是在使用 FunctionExpressions ，例如：

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

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

如果在上例中的第一个函数后省略分号，则会得到完全不希望的结果：

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，因为围绕第二个函数的括号将被解释为函数调用的参数。

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（精彩文章）


• 解释JavaScript封装的匿名函数语法（更多内容 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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