3.5. JavaScript’s New Strict Mode

ECMA-262 version 5 introduced a strict variant, commonly referred to as strict mode, which adds enhanced error checking and security. For example, to help fight against mistyped variable names, variable declarations require the use of the var keyword. Additionally, changes to the eval() function and other areas help JavaScript programmers to improve their code.

Strict mode is enabled with the following syntax, which is very similar to syntax used in Perl: