JavaScript

function validateEmail(email) {
    var regEx = /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/;
    if (regEx.test(email)) {
        return true;
    } else {
        return false;
    }
}

function validate(str)
{
   return str.split('.').length > 1 && str.split('@').length == 2;
};   // validate

function validate(str)
{
   return /\./.test(str) && /^[^@]*@[^@]*$/.test(str);
};   // validate

Compiler is an angular service which traverses the DOM looking for attributes. The compilation process happens into two phases.

Compile: traverse the DOM and collect all of the directives. The result is a linking function.
Link: combine the directives with a scope and produce a live view. Any changes in the scope model are reflected in the view, and any user interactions with the view are reflected in the scope model. Making the scope model a single source of truth.
Some directives such ng-repeat clone DOM elements once for each item in collection. Having a compile and link phase improves performance since the cloned template only needs to be compiled once, and then linked once for each clone instance.

(function (window, document) {
  // we refer to window and document normally
})(window, document);

(function(window){
    var undefined='a';
    console.log(undefined); // prints 'a'
    console.log(window); // prints 'undefined' -> window is defined as 'undefined'
    console.log(a); // throws error (a is undefined).
})(undefined)

(function(undefined){
   console.log(undefined); // prints 'a'
   console.log(a); // throws error (a is undefined).
})('a')

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