Strict Mode is a feature introduced in ES5 that allows you to place a program, or a function, in a “strict” mode.
This strict context prevents certain actions from being taken and throws more exceptions (generally providing the user with more information). Some specific features of strict mode −
Variables not declared but being assigned directly will fail. An attempt to assign foo = "bar"; where ‘foo’ hasn’t been defined will fail.
You cannot use eval in strict mode
You cannot reassign arguments array inside a function
Use of with statements is not allowed
You can use your scripts in strict mode as follows −
Add the following at the top of a script to enable it for the whole script −
"use strict";
If you want to use it only within a function then add it only in that context.
function strictFunc() {
"use strict";
// rest of function
}