(A) The standard way - the Function Definition
This is the std. way a function could be written in Javascript. It's easily recognisable from major programming languages: it has the function keyword, a name, parameters, a function body delimited by curly-braces, and a return.It is also useful to know, or it might just be interesting, that functions are Objects.
function square(x) {
return x * x;
};
Invoked by:
square(5);
(B) Standard function declaration assigned to a variable - the Function Expression
This next example assigns the function to a variable. The interesting here is that you can not invoke the function by the function name. You must invoke it by the variable name.var squareFunction = function square(x) {
return x * x;
};
Invoked by:
squareFunction(5);
Anonymous function
This next one is the Anonymous function. It is a simplification of the previous.The function name is omitted. It is usual to use this anonymous version as it is less verbose, however the previous one can be useful when debugging as the function name will appear in the call stack.
var squareFunction = function (x) {
return x * x;
};
Why the two ways and which one should I use
There are two benefits to using the Function Expression (assigning the function to a var)1. One is it keeps the function name to the local scope and doesn't pollute the global namespace.
2. The name will show up in debuggers.
The immediately invoked anonymous function
The difference is1. Wrap the function in brackets
2. Immediately invoke the function afterwards
( function (x) {
return x * x;
})(numberToSquare);
This is used a lot in jQuery.
