Disallow Initializing to undefined (no-undef-init)

In JavaScript, a variable that is declared and not initialized to any value automatically gets the value of undefined. For example:

var foo;

console.log(foo === undefined);     // true

It’s therefore unnecessary to initialize a variable to undefined, such as:

var foo = undefined;

It’s considered a best practice to avoid initializing variables to undefined.

Rule Details

This rule aims to eliminate variable declarations that initialize to undefined.

The following patterns are considered warnings:

var foo = undefined;
let bar = undefined;

The following patterns are not warnings:

var foo;
let bar;

When Not To Use It

If you want to allow initialization of variables with undefined, then you can safely turn this rule off.


This rule was introduced in ESLint 0.0.6.