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Strict Mode ​

  • JavaScript's "use strict" directive opts scripts or functions into a stricter parsing and error-handling mode. It helps catch common bugs, makes code more secure, and prepares it for future versions of JavaScript.
  • The literal expression "use strict"; instructs the browser to use JavaScript code in strict mode. This also enables block-scoped variables.
  • It prevents accidentally creating a global variable by throwing an error. It also throws an error for assignment to a non-writable property, a getter-only property, a non-existing property, a non-existing variable, or a non-existing object.
  • If you declare strict mode inside a function, it has local scope.
js
x = 3.14; // This will not cause an error.
myFunction();

function myFunction() {
  "use strict";
  y = 3.14; // This will cause an error.
}