Skip to content

Latest commit

 

History

History
71 lines (51 loc) · 1.97 KB

prefer-optional-chain.md

File metadata and controls

71 lines (51 loc) · 1.97 KB
Raw
description
Enforce using concise optional chain expressions instead of chained logical ands, negated logical ors, or empty objects.

🛑 This file is source code, not the primary documentation location! 🛑

See https://typescript-eslint.io/rules/prefer-optional-chain for documentation.

?. optional chain expressions provide undefined if an object is null or undefined. Because the optional chain operator only chains when the property value is null or undefined, it is much safer than relying upon logical AND operator chaining &&; which chains on any truthy value. It is also often less code to use ?. optional chaining than && truthiness checks.

This rule reports on code where an && operator can be safely replaced with ?. optional chaining.

Examples

❌ Incorrect

foo && foo.a && foo.a.b && foo.a.b.c;
foo && foo['a'] && foo['a'].b && foo['a'].b.c;
foo && foo.a && foo.a.b && foo.a.b.method && foo.a.b.method();

// With empty objects
(((foo || {}).a || {}).b || {}).c;
(((foo || {})['a'] || {}).b || {}).c;

// With negated `or`s
!foo || !foo.bar;
!foo || !foo[bar];
!foo || !foo.bar || !foo.bar.baz || !foo.bar.baz();

// this rule also supports converting chained strict nullish checks:
foo &&
  foo.a != null &&
  foo.a.b !== null &&
  foo.a.b.c != undefined &&
  foo.a.b.c.d !== undefined &&
  foo.a.b.c.d.e;

✅ Correct

foo?.a?.b?.c;
foo?.['a']?.b?.c;
foo?.a?.b?.method?.();

foo?.a?.b?.c?.d?.e;

!foo?.bar;
!foo?.[bar];
!foo?.bar?.baz?.();

:::note There are a few edge cases where this rule will false positive. Use your best judgement when evaluating reported errors. :::

When Not To Use It

If you don't mind using more explicit &&s, you don't need this rule.

Further Reading