Why is not recommended to use var

Read this example is estimated that you will understand

    var a = 'global';

    function test() { 
      if (!a) {
        var a = 'part';
      }
      console.log(a);
     }

     test()

 

As a result part, because there are variables declared in advance.

    function test() {
      var a;

      if (!a) {
        a = 'part';
      }
      console.log(a);
    }

When this function is called, will now enhance this function in the initialization of variables.

Therefore, in normal operation, we should minimize the use of var, and let multi const.