对象[foo]术语是什么意思？

I'm confused what the object[foo] term is referring to. Any hints? I know that bar['unique_prop'] and bar.unique_prop refers to 2

我很困惑对象[foo]术语指的是什么。任何提示?我知道bar ['unique_prop']和bar.unique_prop指的是2

    var foo = {unique_prop: 1};
    var bar = {unique_prop: 2};
    var object = {};
    object[foo] = 'value';
    alert(object[bar]);

code on jsfiddle

jsfiddle上的代码

3 个解决方案

#1

This:

var foo = 'abc';
object[foo]

is equivalent to:

相当于:

object.abc

However this:

var foo = {unique_prop: 1};
object[foo] = 'value';

Doesn't have much sense (object property names cannot be object literals). JS engine will use foo.toString() (returning e.g. "[object Object]"), so in fact you are doing this:

没有多大意义(对象属性名称不能是对象文字)。 JS引擎将使用foo.toString()(返回例如“[object Object]”),所以实际上你这样做:

var foo = {unique_prop: 1};
object["[object Object]"] = 'value';

which is clearly a bug or a misunderstanding. This behaviour is explained in Member Operators on MDN:

这显然是一个错误或误解。 MDN上的成员操作员解释了此行为:

Property names must be strings. This means that non-string objects cannot be used as keys in the object. Any non-string object, including a number, is typecasted into a string via the toString method.

属性名称必须是字符串。这意味着非字符串对象不能用作对象中的键。任何非字符串对象(包括数字)都通过toString方法被类型化为字符串。

You can however use:

但是你可以使用:

object[foo.unique_prop] = 'value';

which is equivalent to:

这相当于:

object[1] = 'value';

#2

It is the same as object.whatever_x_is where x is foo.toString() which will be the same as bar.toString() since (unless overridden) calling toString on a generic object will generate a generic "is an object" string such as "[object Object]"

它与object.whatever_x_is相同,其中x是foo.toString(),它与bar.toString()相同,因为(除非被覆盖)在泛型对象上调用toString将生成泛型“is a object”字符串,例如“[object Object]”

#3

object[foo] = 'value';

attempts to use an object as a member name, this causes a .toString() call so;

尝试使用对象作为成员名称,这会导致.toString()调用;

'value' is assigned to object["[object Object]"], when you attempt to read alert(object[bar]); the same toString() occurs as bar is also an object, so you reference object["[object Object]"] once again and get back 'value'.

当您尝试读取alert(object [bar])时,'value'被赋值给object [“[object Object]”];同样的toString()发生,因为bar也是一个对象,所以再次引用对象[“[object Object]”]并返回'value'。

#1