eslint/use-isnan Correctness

What it does

Disallows checking against NaN without using isNaN() call.

Why is this bad?

In JavaScript, NaN is a special value of the Number type. It’s used to represent any of the “not-a-number” values represented by the double-precision 64-bit format as specified by the IEEE Standard for Binary Floating-Point Arithmetic.

Because NaN is unique in JavaScript by not being equal to anything, including itself, the results of comparisons to NaN are confusing:

• NaN === NaN or NaN == NaN evaluate to false
• NaN !== NaN or NaN != NaN evaluate to true

Therefore, use Number.isNaN() or global isNaN() functions to test whether a value is NaN.

Examples

Examples of incorrect code for this rule:

foo == NaN;
foo === NaN;
foo <= NaN;
foo > NaN;

Configuration

This rule accepts a configuration object with the following properties:

enforceForIndexOf

type: boolean

default: false

Whether to disallow NaN as arguments of indexOf and lastIndexOf

enforceForSwitchCase

type: boolean

default: true

Whether to disallow NaN in switch cases and discriminants

How to use

To enable this rule using the config file or in the CLI, you can use:

Config (.oxlintrc.json)

{
  "rules": {
    "use-isnan": "error"
  }
}

CLI

oxlint --deny use-isnan

References

• Rule Source