Explain the encapsulated anonymous function syntax

Question

Summary

Can you explain the reasoning behind the syntax for encapsulated anonymous functions in JavaScript? Why does this work: (function(){})(); but

Answer 1

In javascript, this is called Immediately-Invoked Function Expression (IIFE) .

In order to make it a function expression you've to:

1. enclose it using ()

2. place a void operator before it

3. assign it to a variable.

Otherwise it will be treated as function definition and then you won't be able to call/invoke it at the same time by the following way:

 function (arg1) { console.log(arg1) }(); 

The above will give you error. Because you can only invoke a function expression immediately.

This can be achieved couple of ways: Way 1:

(function(arg1, arg2){
//some code
})(var1, var2);

Way 2:

(function(arg1, arg2){
//some code
}(var1, var2));

Way 3:

void function(arg1, arg2){
//some code
}(var1, var2);

way 4:

  var ll = function (arg1, arg2) {
      console.log(arg1, arg2);
  }(var1, var2);

All above will immediately invoke the function expression.