Using an integer as a key in an associative array in JavaScript

Use an object, as people are saying. However, note that you can not have integer keys. JavaScript will convert the integer to a string. The following outputs 20, not undefined:

var test = {}
test[2300] = 20;
console.log(test["2300"]);

You can just use an object:

var test = {}
test[2300] = 'Some string';

Compiling other answers:

Object

var test = {};

When using a number as a new property's key, the number turns into a string:

test[2300] = 'Some string';
console.log(test['2300']);
// Output: 'Some string'

When accessing the property's value using the same number, the number is turned into a string again:

console.log(test[2300]);
// Output: 'Some string'

When getting the keys from the object, though, they aren't going to be turned back into numbers:

for (var key in test) {
    console.log(typeof key);
}
// Output: 'string'

Map

ECMAScript 6 allows the use of the Map object (documentation, a comparison with Object). If your code is meant to be interpreted locally or the ECMAScript 6 compatibility table looks green enough for your purposes, consider using a Map:

var test = new Map();
test.set(2300, 'Some string');
console.log(test.get(2300));
// Output: 'Some string'

No type conversion is performed, for better and for worse:

console.log(test.get('2300'));
// Output: undefined
test.set('2300', 'Very different string');
console.log(test.get(2300));
// Output: 'Some string'

Use an object instead of an array. Arrays in JavaScript are not associative arrays. They are objects with magic associated with any properties whose names look like integers. That magic is not what you want if you're not using them as a traditional array-like structure.

var test = {};
test[2300] = 'some string';
console.log(test);

Try using an Object, not an Array:

var test = new Object(); test[2300] = 'Some string';

Use an object - with an integer as the key - rather than an array.