Creating new Array in Javascript adds 'unique' key

Question

i'm using a wordpress plugin called DW Question and Answer. I have tried to change some behaviour and stumbled upon this odd problem:

var arr = [];
alert(arr['unique']);

this alerts:

function (){
"use strict";
for(var e=[],i=0;i<this.length;i++)-1==t.inArray(this[i],e)&&e.push(this[i]);return e}

Why is the 'unique' key set with that function?

In another test page on the same system (outside wordpress ) the same code alerts 'undefinded' as expected...

I'm curious to knwo how it is possible to set some keys when creating an empty array.

That's not a key. That's custom Array's method which has been added by the plugin — hindmost
– hindmost, Commented Aug 24, 2014 at 19:00

plalx · Accepted Answer · 2014-08-24 19:07:48Z

1

That's because there's a plugin that modified the native Arrays prototype to add custom members. That's usually a very bad practice.

Still, here's how it's done:

Array.prototype.someMember = 'test';

[].someMember; //test

answered Aug 24, 2014 at 19:07

plalx

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