JavaScript-Interview-Questions/closures.html at master · FADL285/JavaScript-Interview-Questions · GitHub

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<!DOCTYPE html>
<html>
  <head>
    <title>Closures, Lexical Scope and Dynamic Scope</title>
  </head>
  <script>
    /***
     * A closure is the combination of a function bundled together (enclosed) with references
     * to its surrounding state (the lexical environment). In other words, a closure gives
     * you access to an outer function’s scope from an inner function.
     *
     * Lexical Scope:- In lexical scoping free variables must belong to a parent scope.
     *
     * Dynamic Scope:- In dynamic scoping free variables must belong to the calling scope
     *
     * ***/

    var Person = function(name) {
      var text = 'Hello ' + name; // Local variable
      var say = function() {
        // Closure makes this function private to this class
        console.log("Using Closure: "+text);
      };
      return say;
    };

    var obj = new Person('Pradeep');
     obj();


    // ---------------
    // Lexical Scope
    // ---------------
     function add(x) {         // template of a new scope, x is bound in this scope
          return function (y) { // template of a new scope, x is free, y is bound
              return x + y;     // x resolves to the parent scope
          };
      }

      var sum = add(10);      // create a new scope for x and return a function
      console.log("Using Lexical Scope: "+sum(20));         // create a new scope for y and return x + y

  </script>
  <body>
    Closures
  </body>
</html>