JavaScript 中的冒号 (:) 代表什么？

What does the colon (:) in JavaScript represent?

提问by Felix Kling

This is probably a stupid noob question but what does the : represent in the following context:

这可能是一个愚蠢的菜鸟问题，但是 : 在以下上下文中代表什么：

var stuffToDo = {
    'bar' : function() {
        alert('the value was bar -- yay!');
    },

    'baz' : function() {
        alert('boo baz :(');
    },

    'default' : function() {
        alert('everything else is just ok');
    }
};

if (stuffToDo[foo]) {
    stuffToDo[foo]();
} else {
    stuffToDo['default']();
}

Is it storing the function to each of those variables?

是否将函数存储到每个变量中？

回答by Felix Kling

This is an object literal^[MDN]:

这是一个对象文字^[MDN]：

var obj = {
    key: value
};

// obj.key === value; // true

It assigns valueto a property keyof obj. While there are no restriction for what valuecan be (well, it must be something assignable), there are limitations for key: It must be either an identifier name, a string literal or a numeric literal.

它指定value一个属性key的obj。虽然对value可以是什么没有限制（好吧，它必须是可分配的），但有以下限制key：它必须是标识符名称、字符串文字或数字文字。

More details can be found in section 11.1.5of the ECMAScript specification.

更多细节可以在 ECMAScript 规范的11.1.5 节中找到。

The literal notation is similar to:

文字符号类似于：

var stuffToDo = {}; // <-- empty object literal

stuffToDo.bar = function() {...};
// or stuffToDo['bar'] = ...

stuffToDo.baz = function() {...};
// or stuffToDo['baz'] = ...

The biggest difference is that when using an object literal, you cannot access other properties of the object during the declaration.

最大的区别是，在使用对象字面量时，您不能在声明期间访问对象的其他属性。

This will not work:

这将不起作用：

var obj = {
    foo: value,
    bar: obj.foo
};

whereas this does:

而这样做：

var obj = {};
obj.foo = value;
obj.bar = obj.foo;

---

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For completeness, there are two other uses of colons in JavaScript:

为了完整起见，JavaScript 中还有两种冒号的用法：

• Conditional (ternary) operator ^[MDN]:

  var val = condition ? true-value : false-value;
  

• Labels ^[MDN]:

  someLabel: var x = 5;
  

• 条件（三元）运算符^[MDN]：

  var val = condition ? true-value : false-value;
  

• 标签^[MDN]:

  someLabel: var x = 5;
  

回答by gearsdigital

It is the object literal notationhttp://www.dyn-web.com/tutorials/obj_lit.php

它是对象文字符号http://www.dyn-web.com/tutorials/obj_lit.php