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Clarification edit: Creating a new key on an array using arr['key']=1 creates a property on the arr Object but does not add an element to the standard array.
http://stackoverflow.com/questions/8630471/strings-as-keys-o...
var x = [];
console.log(Object.prototype.toString.call(x));
//[object Array]
x[0] = 1;
console.log(x[0]);
//1
x["test"] = 2;
console.log(x["test"]);
//2
console.log(Object.prototype.toString.call(x));
//[object Array]
x.map
//function map() { [native code] }
var y = {};
console.log(Object.prototype.toString.call(y));
//[object Object]
y.map
//undefined x = [1]; x["test"] = 555; x.map(function (y) { return y; });
// [1]
var x = {};
x[0] = 1;
x.length = 1;
x.map = Array.prototype.map;
x.map(function(y) {return y;});
//[1]That is the whole reason prototype.js library broke the use of for (var x in somearray) because the library set properties on Array.prototype.