Question

In the following function:

foo = function(a){
    if (!a) a = "Some value";
    // something done with a
    return a;
}

When “a” is not declared I want to assign a default value for use in the rest of the function, although “a” is a parameter name and not declared as “var a”, is it a private variable of this function? It does not seem to appear as a global var after execution of the function, is this a standard (i.e. consistent) possible use?

Answer 1

It’s a private variable within the function scope. it’s ‘invisible’ to the global scope.
As for your code you better write like this

foo = function(a){
    if (typeof a == "undefined") a = "Some value";
    // something done with a
    return a;
}

Because !a can be true for 0, an empty string '' or just null.