how does this js function work? Title too small to explain

Question

I've been digging into jquery to find out how it works and I see it uses a construct i've never seen in JS before. The following code seems to execute when the browser loads, it's almost like a function that invokes itself. I've searched for docs for this feature but not sure what its called. Can someone tell me the principle so I can google further info on this?

(function test() {
    alert('test');
})();

Answer 1

That's exactly what it is, a self-invoking anonymous function, the variables inside that scope:

(function test() {
  //here
})();

Won't be visible outside unless you expose them either. If you want more detail around uses and practical examples, I'd start with this question.

Answer 2

It is a self-executing function.

It is used to create a local scope. If you have a code-snippet that requires lots of new variables, and you only need to run that code once, then it is a good idea to encapsulate the snippet with this function (so that the variables form the snippet don't pollute the global namespace).

(function() {
    // all variables and functions declared here are not visible
    // outside of this function
})();

However, in your code, the function is not anonymous - you called it "test", so it is a named function expression. It is probably best to not define names for function expressions (because there are bugs in Internet Explorer related to this issue: http://github.com/kangax/nfe