sniff

sniff

This is a simple wrapper to Angus Croll's typeOf function defined in his article Fixing the Javascript typeof operator.

Additionally, it includes a subsequent test to determine whether a function is a functional prototype, and therefore something that would be suitable for calling with the new operator. A value of prototype is returned from the function in event that:

• the target has been detected as a function through Angus's previous logic
• the prototype of the function has some keys defined on it. While this is not a conclusive test (suggestions definitely welcome) I think it covers most of the cases where people are using JS prototypes in their code.

Detecting Function Signature Helper

A small helper has been added to sniff to assist with the process of determining the function signature that a function has been called with. This code was written to help with those cases where you have a function that might be called with a variety of different combinations and permutations.

In simple cases, while you might do something like the following:

function example(name, opts, callback) {
    if (typeof opts == 'function') {
        callback = opts;
        opts = {};
    }
    
    // rest of your function here
}

This can get tiresome and somewhat error prone when you have more complicated functions. This is where the sniff.args helper can come in handy. For example, this next function is designed to be called with just a name, or a name and an age, or name, age and callback, etc, etc. While writing a function like this would probably generally be discouraged in JS every now and again they are needed.

Anyway, let's take a look:

function example(name, age, opts, callback) {
    // first analyse the arguments and get a matcher function
    var matchSig = sniff.args(arguments);

    // check for the name, age and callback case
    if (matchSig('string', 'number|string', 'function')) {
        // remap opts
        callback = opts; 
        opts = {};
    }
    // or the name, opts, function case
    else if (matchSig('string', 'object', 'function')) {
        // remap age, opts, and the callback
        callback = opts,
        opts = age;
        age = null;
    }
}