useAsConstAssertion
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Summary
Section titled “Summary”- Rule available since:
v1.3.0 - Diagnostic Category:
lint/style/useAsConstAssertion - This rule has a safe fix.
- The default severity of this rule is information.
- Sources:
Description
Section titled “Description”Enforce the use of as const over literal type and type annotation.
In TypeScript, there are three common ways to specify that a value is of a specific type such as 2 and not a general type such as number:
as const: telling TypeScript to infer the literal type automaticallyas <literal>: explicitly telling the literal type to TypeScript- type annotation: explicitly telling the literal type to TypeScript when declare variables
The rule suggests to use as const when you’re using as with a literal type or type annotation, since as const is simpler and doesn’t require retyping the value.
Examples
Section titled “Examples”Invalid
Section titled “Invalid”let bar: 2 = 2;code-block.ts:1:10 lint/style/useAsConstAssertion FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
ℹ Use as const instead of type annotation.
> 1 │ let bar: 2 = 2;
│ ^
2 │
ℹ as const doesn’t require any update when the value is changed.
ℹ Safe fix: Replace with as const.
1 │ - let·bar:·2·=·2;
1 │ + let·bar·=·2·as·const;
2 2 │
let foo = { bar: 'baz' as 'baz' };code-block.ts:1:27 lint/style/useAsConstAssertion FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
ℹ Use as const instead of as with a literal type.
> 1 │ let foo = { bar: ‘baz’ as ‘baz’ };
│ ^^^^^
2 │
ℹ as const doesn’t require any update when the asserted value is changed.
ℹ Safe fix: Replace with as const.
1 │ - let·foo·=·{·bar:·‘baz’·as·‘baz’·};
1 │ + let·foo·=·{·bar:·‘baz’·as·const·};
2 2 │
let foo = 'bar';let foo = 'bar' as const;let foo: 'bar' = 'bar' as const;let bar = 'bar' as string;let foo = { bar: 'baz' };How to configure
Section titled “How to configure”{ "linter": { "rules": { "style": { "useAsConstAssertion": "error" } } }}