How to prevent using only numbers if/else conditions (an ESLint rule?): e.g. if (myNumber) { /* ... */ }

Question

I've recently found multiple bugs related to values being 0 in if/else statements. They were being handled as if they're false.

For example,

  if (viewState.latitude) { // 👈🏼️ I needed to add a !== undefined to handle when latitude is 0
    params.set(
      QUERY_PARAM_LATITUDE_KEY,
      viewState.latitude.toFixed(4).toString(),
    );
  }

How can I prevent these? I can't find an ESLint rule for this. It would be nice if I could prevent if (number) { formats. It seems like a really simple question though 🤷🏼️

Answer 1

strict-boolean-expressions

Enabling this rule does make things more verbose. It has already caught more bugs though. It really is a tradeoff.

  if (viewState.latitude) {
    params.set(
      QUERY_PARAM_LATITUDE_KEY,
      viewState.latitude.toFixed(4).toString(),
    );
  }

will error with

Unexpected nullable number value in conditional. Please handle the nullish/zero/NaN cases explicitly  @typescript-eslint/strict-boolean-expressions`.

More verbose

Note: rightButton is a boolean | undefined

// previously
if (event.rightButton) {
// now
if (event.rightButton !== undefined && event.rightButton) {
// or alternatively
if (event.rightButton === true) {

Eslint config

module.exports = {
  "rules": {
    "@typescript-eslint/strict-boolean-expressions": "error"
  }
};