javascript - 为什么有些对象文字属性被引用而有些则没有？

Question

这个问题在这里已经有了答案:

What is the difference between object keys with quotes and without quotes? (5 个回答)

关闭 9年前.

我经常看到这种情况:对象字面量的声明使得一些键用引号括起来，而另一些则没有。一个来自 jQuery 1.4.2 的例子:

jQuery.props = {
    "for": "htmlFor",
    "class": "className",
    readonly: "readOnly",
    maxlength: "maxLength",
    cellspacing: "cellSpacing",
    rowspan: "rowSpan",
    colspan: "colSpan",
    tabindex: "tabIndex",
    usemap: "useMap",
    frameborder: "frameBorder"
};

将前两个属性键(for 和 class)用引号括起来有什么意义无报价？有什么区别吗？

我一直在寻找 ECMAScript 5 specification ;我所能找到的只是 [第 15.12.3 节的注 6，重点是我的]:

NOTE 6 An object is rendered as an opening left brace followed by zero or more properties, separated with commas, closed with a right brace. A property is a quoted String representing the key or property name, a colon, and then the stringified property value. An array is rendered as an opening left bracket followed by zero or more values, separated with commas, closed with a right bracket.

不过，这里只指JSON的字符串化。

Answer 1

这些是 Javascript 保留字，并且(虽然不是真的必要)语言的语法要求它们被引用。

严格来说，纯“JSON”表示法要求所有的“键”字符串都被引用。然而，Javascript 本身可以使用不带引号的有效标识符(但不是保留字)的键。