JavaScript Use Strict

Conclusion

The strict mode makes it easier to write “secure” JavaScript. It changes previously accepted “bad syntax” into real errors. For example, in regular, JavaScript, mistyping the variable name creates the new global variable. In strict mode, it results in error, making it impossible to create the global variable accidentally.

In standard JavaScript, the developer will not receive any error feedback assigning values to the non-writable properties. In strict mode, any assignment to the non-writable property, a getter-only property, a non-existing property, the non-existing variable, or the non-existing object, will throw an error.

Keywords reserved for future JavaScript versions cannot be used as the variable names in strict mode. Those keywords are the following : implements, interface, let, package, private, protected, public, static, yield.

In case we are using browser console to test any feature, by default strict mode is not enforced. We need to add manually by using ‘use strict’.