Q: What are the characteristics of JavaScript ‘Strict Mode’?

‘Strict Mode is a new feature in ECMAScript 5 that allows you to place a program, or a function, in a “strict” operating context. This strict context prevents certain actions from being taken and throws more exceptions. The statement “use strict”; instructs the browser to use the Strict mode, which is a reduced and safer feature set of JavaScript.

Answer: Given below are the characteristics of JavaScript ‘Strict Mode’:

• ‘Strict Mode’ will stop developers from creating global variables.
• Developers are restricted from using duplicate parameters.
• Strict mode will restrict you from using JavaScript keyword as a variable name or function name.
• Strict mode is declared with ‘use strict’ keyword at the beginning of the script.
• All browser support strict mode.

Example:

Without using strict mode you can use variable without declearing it:-
x = 10;
console.log(x);
//Text in console = 10

When you strict mode you can't use variable without declearing it:-
'use strict'; x = 10;
console.log(x);
//error: Uncaught ReferenceError: x is not defined