Very often in javascript some function parameters are optional. So, code like this become needed:
if (typeof something == "undefined")
alert("something is undefined");
However, there is a better, slicker solution. This is a null coalescing operator in javascript "terms":
function DoSomething(element)
{
element = element || document.body;
}
function DoSomething(index)
{
index = index || 0;
}
In example above element variable gets value of document.body if null (undefined). Similarly index variable gets 0 value if undefined or null.