JavaScript use strict

When you use the "use strict" directive in JavaScript, a strict mode is enabled, ensuring that you comply with stricter rules and handle errors better. Activating strict mode prevents or flags certain JavaScript behaviors that are deemed problematic or error-prone.

Syntax

'use strict';
// Your code here

Using the "use strict" directive at the top of your JavaScript file or script tag will activate strict mode in your script.

Without use strict

str = 'abc';
console.log(str); // abc

Appling use strict

'use strict';
str = 'abc';
console.log(str); ReferenceError: str is not defined

Example: Function-level strict mode

function myFunction() {
  "use strict";
  // Your code here
 }

Here, strict mode is only active within the myFunction function. By doing this, you can apply strict mode selectively to specific functions, even if the rest of the script is not.

Example: Strict mode for specific scope

function outerFunction() {
    // Non-strict mode
    
    function innerFunction() {
      "use strict";
      
      // Strict mode enabled for this function
      
      // Your code here
    }
    
    // Non-strict mode
    
    // Your code here
  }