use strict mode is used in javascript for code example

Example 1: strict mode in javascript

/*
even though x is not defined with a keyword like var, let or const, the
browser won't throw an error
*/
x = 1;

function myFunc() {
  "use strict";
  
  /*
  this will throw an error as y is being assigned a value without it 
  being declared AND "use strict" has been used for the function
  */
  y = 4;
}

/*
Basically, "use strict" is a way for programmers to avoid bad habits by using
invalid syntax which browsers accept but is still wrong
*/

Example 2: use strict javascript

// Non-strict code...

(function(){
  "use strict";

  // Define your library strictly...
})();

// Non-strict code...