eslint/no-constant-binary-expression Correctness
What it does
Disallow expressions where the operation doesn't affect the value.
Why is this bad?
Comparisons which will always evaluate to true or false and logical expressions (||, &&, ??) which either always short-circuit or never short-circuit are both likely indications of programmer error. By default, this rule also reports relational comparisons (<, <=, >, >=) where both sides are literal values.
These errors are especially common in complex expressions where operator precedence is easy to misjudge.
Additionally, this rule detects comparisons to newly constructed objects/arrays/functions/etc. In JavaScript, where objects are compared by reference, a newly constructed object can never === any other value. This can be surprising for programmers coming from languages where objects are compared by value.
Examples
Examples of incorrect code for this rule:
// One might think this would evaluate as `a + (b ?? c)`:
const x = a + b ?? c;
// But it actually evaluates as `(a + b) ?? c`. Since `a + b` can never be null,
// the `?? c` has no effect.
// Programmers coming from a language where objects are compared by value might expect this to work:
const isEmpty = x === [];
// However, this will always result in `isEmpty` being `false`.Examples of correct code for this rule:
const x = a + (b ?? c);
const isEmpty = x.length === 0;Configuration
This rule accepts a configuration object with the following properties:
checkRelationalComparisons
type: boolean
default: true
How to use
To enable this rule using the config file or in the CLI, you can use:
{
"rules": {
"no-constant-binary-expression": "error"
}
}import { defineConfig } from "oxlint";
export default defineConfig({
rules: {
"no-constant-binary-expression": "error",
},
});oxlint --deny no-constant-binary-expressionVersion
This rule was added in v0.0.3.