exhaustiveCheck - API reference

API reference › @evolu/common › Function › exhaustiveCheck

function exhaustiveCheck(value: never): never;

Defined in: packages/common/src/Function.ts:95

Helper function to ensure exhaustive matching in a switch statement. Throws an error if an unhandled case is encountered.

Example

import { exhaustiveCheck } from "@evolu/common";

type Color = "red" | "green" | "blue";
const handled: Array<string> = [];

const handleColor = (color: Color): void => {
  switch (color) {
    case "red":
      handled.push("Handling red");
      break;
    case "green":
      handled.push("Handling green");
      break;
    case "blue":
      handled.push("Handling blue");
      break;
    default:
      exhaustiveCheck(color);
  }
};

handleColor("blue");
expect(handled).toEqual(["Handling blue"]);

Use this primarily in side-effect switches (void branches). For value-producing switches, TypeScript can enforce exhaustiveness without a default branch in either of the following styles.

Assign in every case

type Input =
  | { readonly type: "Mutate" }
  | { readonly type: "Query" }
  | { readonly type: "Export" };

const inputToKind = (input: Input): "A" | "B" | "C" => {
  let result: "A" | "B" | "C";

  switch (input.type) {
    case "Mutate":
      result = "A";
      break;
    case "Query":
      result = "B";
      break;
    case "Export":
      result = "C";
      break;
  }

  return result;
};

expect(inputToKind({ type: "Query" })).toBe("B");