How should I generate unique IDs for a bunch of objects?

Question

I have an array consisting of A LOT of Symbol objects:

var symbols = {
    alpha : new Symbol('alpha', 'symbol_0', '&#x03B1', 'GreekSymbol'),
    beta : new Symbol('beta', 'symbol_1', '&#x03B2', 'GreekSymbol'),
    gamma : new Symbol('gamma', 'symbol_2', '&#x03B3', 'GreekSymbol'),
    delta : new Symbol('delta', 'symbol_3', '&#x03B4', 'GreekSymbol'),

    ... about 500 of these different types of symbols...
};

The second parameter for the Symbol object is an ID that will be used in HTML. Since the HTML specs don't allow duplicate IDs, I want to assign each Symbol a unique ID and still be able to know that this ID corresponds to a Symbol. So I like the idea of having the symbol_ prefix but I don't like the idea of manually typing out symbol_0 through symbol_500.

How should I generate unique IDs? Can I automate this process and generate a unique ID when I'm declaring the above array?

UPDATE
Is it actually a good idea to do this client-side?

Answer 1

Make a function that increments a counter:

function makeCounter() {
    var i = 0;
    return function() {
        return i++;
    }
}

var id = makeCounter();

Now each call to id will return a unique value:

id(); // 0
id(); // 1
id(); // 2
id(); // 3

Use it like this:

new Symbol('alpha', 'symbol_' + id(), '&#x03B1,', 'GreekSymbol')

A more fully-featured version would allow you to specify the prefix and an optional start value:

function generateId(prefix, start) {
    var i = start || 0;
    return function() {
        return prefix + i++;
    }
}
// start the counter at 12
var id = generateId("symbol_", 12);
id();

Output:

"symbol_12"

Answer 2

A simple object that keeps track of the number of calls should work.

function IdGenerator(baseName) {
    this.baseName = "" + baseName;
    this.number = 0;
}

IdGenerator.prototype.next = function () {
    return "" + this.baseName + this.number++;
};

var gen = new IdGenerator("symbol_")
for (var i = 0; i < 100; i++) {
    console.log(gen.next());
}