Closures in JavaScript

Closures are inner functions declared within outer functions.

function outerFunction(passedParameters) {
    //closure
    function(passedParams2) {
        //closure code
    }
}

Closures have access to variables declared in the outer function, as well as global variables.

function square(number) {
    function multiply(a, b) {
        return a * b;
    }
    return multiply(number, number);
}