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switch-exhaustiveness-check

Require switch-case statements to be exhaustive.

💡

Some problems reported by this rule are manually fixable by editor suggestions.

💭

This rule requires type information to run.

When working with union types or enums in TypeScript, it's common to want to write a switch statement intended to contain a case for each constituent (possible type in the union or the enum). However, if the union type or the enum changes, it's easy to forget to modify the cases to account for any new types.

This rule reports when a switch statement over a value typed as a union of literals or as an enum is missing a case for any of those literal types and does not have a default clause.

There is also an option to check the exhaustiveness of switches on non-union types by requiring a default clause.

.eslintrc.cjs
module.exports = {
  "rules": {
    "@typescript-eslint/switch-exhaustiveness-check": "error"
  }
};
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Examples​

When the switch doesn't have exhaustive cases, either filling them all out or adding a default will correct the rule's complaint.

Here are some examples of code working with a union of literals:

type Day =
  | 'Monday'
  | 'Tuesday'
  | 'Wednesday'
  | 'Thursday'
  | 'Friday'
  | 'Saturday'
  | 'Sunday';

declare const day: Day;
let result = 0;

switch (day) {
  case 'Monday':
    result = 1;
    break;
}
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Likewise, here are some examples of code working with an enum:

enum Fruit {
  Apple,
  Banana,
  Cherry,
}

declare const fruit: Fruit;

switch (fruit) {
  case Fruit.Apple:
    console.log('an apple');
    break;
}
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Options​

This rule accepts the following options

type Options = [
  {
    /** If 'true', require a 'default' clause for switches on non-union types. */
    requireDefaultForNonUnion?: boolean;
  },
];

const defaultOptions: Options = [{ requireDefaultForNonUnion: false }];

requireDefaultForNonUnion​

Examples of additional incorrect code for this rule with { requireDefaultForNonUnion: true }:

const value: number = Math.floor(Math.random() * 3);

switch (value) {
  case 0:
    return 0;
  case 1:
    return 1;
}
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Since value is a non-union type it requires the switch case to have a default clause only with requireDefaultForNonUnion enabled.

When Not To Use It​

If you don't frequently switch over union types or enums with many parts, or intentionally wish to leave out some parts.

Resources​