@rushstack/eslint-plugin

This plugin implements supplementary rules for use with the @rushstack/eslint-config package, which provides a TypeScript ESLint ruleset tailored for large teams and projects. Please see [that project's documentation](@rushstack/eslint-config) for details. To learn about Rush Stack, please visit: https://rushstack.io/

@rushstack/no-null

Prevents usage of JavaScript's null keyword.

Rule Details

Most programming languages have a "null" or "nil" value that serves several purposes:

1. the initial value for an uninitialized variable
2. the value of x.y or x["y"] when x has no such key, and
3. a special token that developers can assign to indicate an unknown or empty state.

In JavaScript, the undefined value fulfills all three roles. JavaScript's null value is a redundant secondary token that only fulfills (3), even though its name confusingly implies otherwise. The null value was arguably a mistake in the original JavaScript language design, but it cannot be banned entirely because it is returned by some entrenched system APIs such as JSON.parse(), and also some popular NPM packages. To avoid requiring lint suppressions when interacting with these legacy APIs, this rule prohibits null as a literal value, but not in type annotations. Comparisons with null are also allowed. In other words, this rule aims to tolerate preexisting null values but prevents new ones from being introduced.

Examples

The following patterns are considered problems when @rushstack/no-null is enabled:

let x = null;  // error

f(null); // error

function g() {
    return null; // error
}

The following patterns are NOT considered problems:

let x: number | null = f(); // declaring types as possibly "null" is okay

if (x === null) {  // comparisons are okay
    x = 0;
}