JavaScript在对象键值对中删除数组括号

Question

Hey guys I noticed something strange today with trying to set a key value pair in JavaScript. I know that The Key of an object is always 'stringified' so that the key value pair is always string: value, however something strange happened today when I tried this with an array. Example below:

var ob = {}; 

var a = [2,4]; 

ob[a] = 10; 

console.log("this is ob ", ob);

Here I have tried adding the key [2,4] to map to 10. However, the console log returns the string 2,4 mapping to 10 instead of the string [2,4] mapping to 10. Does anyone know why this happens?

Answer 1

Using an object or an array as the property name, doesn't invoke JSON#stringify , but the object's toString method, which in arrays returns the array elements joined by a comma.

In the example I override the Array#toString method, and you can see that the resulting property name reflects that:

 var ob = {}; var a = [2,4]; a.toString = function() { return 'cats' }; // override toString ob[a] = 10; console.log("this is ob ", ob);