Question

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JavaScript: Why the anonymous function wrapper?

I would like to ask you what is the reason of wrapping everything in

(function() {
  document.write("Hello World!");
})(); 

function?

Answer 1

Self executing anonymous function’s main purpose is to wrap everything in a private namespace, meaning any variables declared do not pollute the global namespace, basically like a sandbox.

var test = 1;

test would pollute the global namespace, window.test would be set.

(function() {
    var test = 1; alert( test );
})();

window.test is undefined, because it’s in our private sandbox.