JS mimic block-level scope

        var  5 ;         var   i;        alert (i);

When a variable is declared assigned, if it is declared again, it will not change the value after the last assignment, so the value of I is still 5, only after the value is re-assigned, such as:

        var 5 ;         var 6 ;        alert (i);

I now the value is 6;

There is no block-level scope in JS, if you want the effect of block-level scope, you can imitate, such as:

(function () {            for (var05; i++) {             }        }) ();         // Error

This method can be understood to put block-level scopes in an anonymous function, so the variables declared in the anonymous function are automatically cleaned up after the execution of the function is completed. In addition, this approach reduces the memory problems that are used by closures because there is no reference to the anonymous function being executed.

JS mimic block-level scope