#no-extra-boolean-cast

#Configuration

import { defineConfig, js } from '@rslint/core';

export default defineConfig([
  js.configs.recommended,
  {
    rules: {
      'no-extra-boolean-cast': 'error',
    },
  },
]);

#Rule Details

Disallows unnecessary boolean casts. Using !! (double negation) or Boolean() to convert a value to boolean is redundant when the value is already in a boolean context, such as the test of an if statement.

new Boolean(x) is never flagged because it produces a Boolean object (always truthy) rather than a primitive, so replacing it with a plain value would change semantics.

Examples of incorrect code for this rule:

if (!!foo) {
}
while (!!foo) {}
do {} while (!!foo);
for (; !!foo; ) {}
!!foo ? bar : baz;
!!!foo;
if (Boolean(foo)) {
}
!Boolean(foo);

Examples of correct code for this rule:

if (foo) {
}
while (foo) {}
var bar = !!foo;
var bar = Boolean(foo);
function baz() {
  return !!foo;
}
if (new Boolean(foo)) {
} // always truthy — not equivalent to `if (foo)`

#Options

This rule accepts a single options object.

#enforceForLogicalOperands (legacy)

When true, the rule also reports redundant boolean casts that are operands of || or && when the overall logical expression is used in a boolean context.

{ "no-extra-boolean-cast": ["error", { "enforceForLogicalOperands": true }] }

if (x || !!y) {
} // reported

#enforceForInnerExpressions

A superset of enforceForLogicalOperands. Additionally reports redundant casts on the right-hand side of ??, on the branches of ternaries, and on the last expression of a sequence (a, b, c).

{ "no-extra-boolean-cast": ["error", { "enforceForInnerExpressions": true }] }

if (x ?? !!y) {
} // reported
if (cond ? Boolean(a) : b) {
} // reported
if ((a, b, Boolean(c))) {
} // reported

#Original Documentation

• ESLint no-extra-boolean-cast