typescript/no-duplicate-type-constituents Correctness
What it does
This rule disallows duplicate constituents of union or intersection types.
Why is this bad?
Duplicate constituents in union and intersection types serve no purpose and can make code harder to read. They are likely a mistake.
Examples
Examples of incorrect code for this rule:
ts
type T1 = "A" | "A";
type T2 = A | A | B;
type T3 = { a: string } & { a: string };
type T4 = [A, A];
type T5 = "foo" | "bar" | "foo";Examples of correct code for this rule:
ts
type T1 = "A" | "B";
type T2 = A | B | C;
type T3 = { a: string } & { b: string };
type T4 = [A, B];
type T5 = "foo" | "bar" | "baz";Configuration
This rule accepts a configuration object with the following properties:
ignoreIntersections
type: boolean
default: false
Whether to ignore duplicate types in intersection types. When true, allows type T = A & A.
ignoreUnions
type: boolean
default: false
Whether to ignore duplicate types in union types. When true, allows type T = A | A.
How to use
To enable this rule using the config file or in the CLI, you can use:
json
{
"options": {
"typeAware": true
},
"rules": {
"typescript/no-duplicate-type-constituents": "error"
}
}ts
import { defineConfig } from "oxlint";
export default defineConfig({
options: { typeAware: true },
rules: {
"typescript/no-duplicate-type-constituents": "error",
},
});bash
oxlint --type-aware --deny typescript/no-duplicate-type-constituentsVersion
This rule was added in v1.12.0.