src/content/docs/linter/rules/no-unnecessary-conditions.mdx
import { Tabs, TabItem } from '@astrojs/starlight/components';
<Tabs> <TabItem label="JavaScript (and super languages)" icon="seti:javascript"> :::caution This rule is part of the [nursery](/linter/#nursery) group. This means that it is experimental and the behavior can change at any time. ::: :::note This rule belongs to the types domain. This means that its activation will activate the Biome Scanner to scan the files of your project, and enable the type inference engine. Read more about it in the [documentation page](/linter/domains#types) ::: ## Summary - Rule available since: `v2.1.4` - Diagnostic Category: [`lint/nursery/noUnnecessaryConditions`](/reference/diagnostics#diagnostic-category) - This rule doesn't have a fix. - The default severity of this rule is [**warning**](/reference/diagnostics#warning). - This rule belongs to the following domains: - [`types`](/linter/domains#types) - Sources: - Inspired from [`@typescript-eslint/no-unnecessary-condition`](https://typescript-eslint.io/rules/no-unnecessary-condition){
"linter": {
"rules": {
"nursery": {
"noUnnecessaryConditions": "error"
}
}
}
}
Disallow unnecessary type-based conditions that can be statically determined as redundant.
This rule detects if expressions inside conditions are statically inferrable and yield falsy or truthy values that don't change during the life cycle of the program.
function head<T>(items: T[]) {
if (items) { // This check is unnecessary
return items[0].toUpperCase();
}
}
function foo(arg: 'bar' | 'baz') {
if (arg) { // This check is unnecessary
}
}
function bar(arg: string) {
return arg?.length; // ?. is unnecessary
}
Contrary to the source rule, this rule doesn't trigger bindings that are assigned to multiple
values. In the following example, the variable greeting is assigned to multiple values; hence
it can't be inferred to a truthy or falsy value.
let greeting = false;
function changeGreeting() {
greeting = "Hello World!"
}
if (greeting) {} // rule not triggered here
function head<T>(items: T[] | null) {
if (items) { // This check is necessary
return items[0].toUpperCase();
}
}
function foo(arg: 'bar' | 'baz' | null) {
if (arg) { // This check is necessary
}
}
function bar(arg: string | undefined) {
return arg?.length; // ?. is necessary
}