Strict mode in JavaScript

What is strict mode?

• Strict mode was introduced in ECMAScript5 also known as ES5 in 2009.
• Adding strict mode to JavaScript code allows your code to be checked more strictly.
• Allows programmer to write more secure JavaScript code.

Benefits of Strict Mode

• Using strict mode in JavaScript code throws visible errors in developer console which would otherwise fail silently (shown in the examples below).
• Forbids programmers to use certain syntax.
• In some cases using strict mode in code can make the code to run faster.

How to enable strict mode in JavaScript?

• To enable strict mode write "use strict" or 'use strict' at the beginning of JavaScript code.
  

• The strict mode can also be used for a function.

• To enable strict mode in function, "use strict" or 'use strict' must be the very first line in function body.
  

Common mistakes that occur in non-strict mode

Using reserved words as variable names

• Wait!! Isn't "let" a reserved word in the JavaScript? Therefore it mustn't be used as a variable name according to naming an identifier rules. Here in the above code snippet JavaScript fails silently instead of throwing an error.
• But, if we use strict mode, JavaScript engine will throw an error-

Using variables before declaring them

• Using strict mode gives Reference Error.
  
  

• To know more about the strict mode, checkout the documentation by MDN

Conclusion

• That will be all from my side. I hope, this article gave you a basic idea about the strict mode.

Keep Learning!!