Question

When building a jQuery plugin that is supposed to be passed a Boolean value, what’s the most fool-proof way of converting the input to a Boolean in a user-friendly way?

To be more precise: I am afraid of the case that people might pass a String of 'false' (instead of a plain false) and therefore a simple conversion of !!option or Boolean(option) will return the “wrong” value (!!'false' is true).

At the moment I am checking my var option like this:

if (typeof(option) != 'boolean'){
    if (option === 'false'){
        option = false; //fake false
    } else {
        option = !!option; //everything else is converted as truthy / falsy in a standard manner  
    }
}

but I was wondering if there is a more elegant and concise way to do so, or is this just the way that JavaScript handles this?

Answer 1

The most fool proof way, if you are afraid of such input, is to do just

if (typeof(option) != 'boolean')
    console.error('Function X expects a Boolean.');

Look at the solution you have now, you didn’t take into account 0 or 1. Or what about no or yes?

Strings and Integers aren’t meant to be used as Booleans; so, there is no need to parse them.

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Take a look at high quality / usage JS frameworks, they don’t do this. Why should you?