What's the big O for JavaScript's array when used as a hash?

Question

What\'s the big O for JavaScript\'s array access when used as a hash?

For example,

var x= [];
for(var i=0; i<100000; i++){
   x[i.toString()+\'a\'         


        

Answer 1

First and foremost Arrays are in fact hashes. Always. That's why x[5] === x["5"]:

var x = [];
x[5] = 10;
alert( x[5] === x["5"] ); // true

Objects are hashes and Arrays are just special objects. If you want to use general hashes go for Objects. "Associative arrays" in Javascript are Objects. Arrays are for numerically indexed data. Arrays have a length property and Array-like methods like push, pop, sort, etc. which makes no sense to be used on hashes.

As for the big O for searching in Objects: it's implementation dependent.

Probably the 2 best things you can do to:

1. Check the source code of some browser implementations

2. Do some benchmark for big n and make your conclusion

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The related part of the language specification:

4.3.3 object

An object is a collection of properties and has a single prototype object.

8.6.2 Object Internal Properties and Methods

Array objects have a slightly different implementation of the [[DefineOwnProperty]] internal method. Array objects give special treatment to a certain class of property names.