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no-redeclare

Disallow variable redeclaration.

Examples​

This rule extends the base eslint/no-redeclare rule. It adds support for TypeScript function overloads, and declaration merging.

How to Use​

.eslintrc.cjs
module.exports = {
  "rules": {
    // Note: you must disable the base rule as it can report incorrect errors
    "no-redeclare": "off",
    "@typescript-eslint/no-redeclare": "error"
  }
};
Try this rule in the playground ↗

Options​

See eslint/no-redeclare options.

This rule adds the following options:

interface Options extends BaseNoRedeclareOptions {
  ignoreDeclarationMerge?: boolean;
}

const defaultOptions: Options = {
  ...baseNoRedeclareDefaultOptions,
  ignoreDeclarationMerge: true,
};

ignoreDeclarationMerge​

When set to true, the rule will ignore declaration merges between the following sets:

  • interface + interface
  • namespace + namespace
  • class + interface
  • class + namespace
  • class + interface + namespace
  • function + namespace
  • enum + namespace

Examples of correct code with { ignoreDeclarationMerge: true }:

interface A {
  prop1: 1;
}
interface A {
  prop2: 2;
}

namespace Foo {
  export const a = 1;
}
namespace Foo {
  export const b = 2;
}

class Bar {}
namespace Bar {}

function Baz() {}
namespace Baz {}

Note: Even with this option set to true, this rule will report if you name a type and a variable the same name. This is intentional. Declaring a variable and a type and a variable the same is usually an accident, and it can lead to hard-to-understand code. If you have a rare case where you're intentionally naming a type the same name as a variable, use a disable comment. For example:

type something = string;
// eslint-disable-next-line @typescript-eslint/no-redeclare -- intentionally naming the variable the same as the type
const something = 2;

Resources​

Taken with ❤️ from ESLint core