Question

I’m building an Entity System in Javascript. It’s basically a technique of composing in-world objects out of components, like “Position”, or “Sprite”. These components only hold data, and they have only minor methods.

I’m implementing it in a sort of database, the entity is just an id for getting to instances of components.

The “database” is a dictionary, that will look like this:

{
    "ComponentType": ComponentInstances
}

A Component instance is accesed like this: db[componentType][entityId].

I’m concerned as to what data type would be the most efficient for for entityId: a string or a number? How much memory do these types take in Javascript (I know it varies, but even an estimation would be useful)?

Of course, if it was a string, the database would be implemented like a dictionary-of-dictionaries, and if it was a number, a dictionary-of-arrays (which doesn’t matter because both are objects).

Edit: compared to a reference, how much memory heavy are strings and numbers? Are they more efficient?

Answer 1

While conceptually both numbers and strings are treated the same when used as keys (keys are always treated as strings in Javascript – x[0] and x[“0”] return the same value), most recent implementations will special case the numeric keys and store them in a contiguous array.

Therefore, I would go for contiguous numeric indexes if I were you.