Why JavaScript function declaration (and expression)?

Question

I've seen others using the following pattern.

var bar = function foo(){};
console.log(bar); // foo()
console.log(foo); // ReferenceError: foo is not defined

But why? I can see the point if both were declared, but they're not. Why is the reason?

Answer 1

As mentioned by others, using the first form in your example (a named function expression) can help with debugging, although with the recent improvements in built-in developer tools in browsers, this argument is becoming less persuasive. The other reason for using a named function expression is that you can use the function name as a variable within the body of the function rather than the now-deprecated in ES5 arguments.callee.

However, named function expressions are incorrectly and problematically implemented in Internet Explorer < 9 and should generally be avoided when you're targeting those browsers. See Juriy Zaytsev's excellent article on the subject for more information.