What is the strict mode of JS

Reasons for setting up a strict model:

-Eliminate some of the unreasonable and less rigorous JavaScript syntax, and reduce some of the bizarre behavior;

-Eliminate some of the unsafe code operation, to ensure the security of code operation;

-Improve the efficiency of the compiler, increase the speed of operation;

-Pave the future for new versions of JavaScript.

"Strict mode" embodies JavaScript more reasonable, more secure, more rigorous development direction

"Use strict";//is a sign of entering strict mode

Changes in grammar and behavior

1. Explicit declaration of global variables

Strict mode

            ' Use strict ';            A=2;            Console.log (a)// error for            (i=0;i<5;i++) {  // error                 Console.log (i)            }

Normal mode

            a=2;            Console.log (a)//2for            (i=0;i<5;i++) {                Console.log (i)  //0 1 2 3 4            }

Reference: http://www.ruanyifeng.com/blog/2013/01/javascript_strict_mode.html

What is the strict mode of JS