Why is 'use strict' used in JavaScript?

'use strict'` is a directive that enables strict mode in JavaScript.

Strict mode:

• Prohibits the use of undeclared variables.
• Disables implicit binding of this to the global object in functions.
• Throws errors when assigning to read-only properties.
• Prevents deleting non-deletable properties.
• Disables with.
• Prohibits duplicate parameter names in functions.
• Simplifies code optimization.

Advantages of using 'use strict':

• Improves code readability and maintainability: Detects potential errors early.
• Prevents accidental errors: Disallows dangerous or undesirable constructs.
• Ensures future compatibility: Some features of future JavaScript versions may require strict mode.

Strict mode can be applied to an entire script or individual functions by placing the directive at the first line.

// Applying to a function
function myStrictFunction() {
  'use strict';
  // Code in strict mode
}

// Applying to the entire script
// Must be the first line of the file
'use strict';
// Code in strict mode