How to check if function exists in JavaScript?

I had this problem. if (obj && typeof obj === 'function') { ... } kept throwing a reference error if obj happened to be undefined, so in the end I did the following:

if (typeof obj !== 'undefined' && typeof obj === 'function') { ... }

However, a colleague pointed out to me that checking if it's !== 'undefined' and then === 'function' is redundant, thus:

Simpler:

if (typeof obj === 'function') { ... }

Much cleaner and works great.

Try something like this:

if (typeof me.onChange !== "undefined") { 
    // safe to use the function
}

or better yet (as per UpTheCreek upvoted comment)

if (typeof me.onChange === "function") { 
    // safe to use the function
}