noUnnecessaryConditions

JavaScript (and super languages)

Summary

Rule available since: v2.1.4
Diagnostic Category: lint/nursery/noUnnecessaryConditions
This rule doesn’t have a fix.
The default severity of this rule is warning.
This rule belongs to the following domains:
- project
Sources:
- Inspired from @typescript-eslint/no-unnecessary-condition

How to configure

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{
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  "linter": {
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    "rules": {
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      "nursery": {
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        "noUnnecessaryConditions": "error"
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      }
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    }
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  }
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}

Description

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.

Examples

Invalid

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function head<T>(items: T[]) {
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  if (items) {  // This check is unnecessary
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    return items[0].toUpperCase();
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  }
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}

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function foo(arg: 'bar' | 'baz') {
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  if (arg) {  // This check is unnecessary
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  }
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}

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function bar(arg: string) {
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  return arg?.length;  // ?. is unnecessary
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}

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.

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let greeting = false;
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function changeGreeting() {
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    greeting = "Hello World!"
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}
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if (greeting) {} // rule not triggered here

Valid

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function head<T>(items: T[] | null) {
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  if (items) {  // This check is necessary
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    return items[0].toUpperCase();
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  }
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}

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function foo(arg: 'bar' | 'baz' | null) {
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  if (arg) {  // This check is necessary
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  }
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}

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function bar(arg: string | undefined) {
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  return arg?.length;  // ?. is necessary
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}