devsite/node_modules/assert-never/index.ts

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2024-07-08 01:49:38 +00:00
export function assertNever(value: never, errorMessage?: string): never
export function assertNever(value: never, getErrorMessage?: (value: unknown) => string): never
export function assertNever(value: never, noThrow?: boolean): never
/**
* Helper function for exhaustive checks of discriminated unions.
* https://basarat.gitbooks.io/typescript/docs/types/discriminated-unions.html
*
* @example
*
* type A = {type: 'a'};
* type B = {type: 'b'};
* type Union = A | B;
*
* function doSomething(arg: Union) {
* if (arg.type === 'a') {
* return something;
* }
*
* if (arg.type === 'b') {
* return somethingElse;
* }
*
* // TS will error if there are other types in the union
* // Will throw an Error when called at runtime.
* // Use `assertNever(arg, true)` instead to fail silently.
* return assertNever(arg);
* }
*/
export function assertNever(value: never, errorMessageOrNoThrow?: string | ((value: unknown) => string) | boolean): never {
if (typeof errorMessageOrNoThrow === 'string') {
throw new Error(errorMessageOrNoThrow)
}
if (typeof errorMessageOrNoThrow === 'function') {
throw new Error(errorMessageOrNoThrow(value))
}
if (errorMessageOrNoThrow) {
return value
}
throw new Error(
`Unhandled discriminated union member: ${JSON.stringify(value)}`,
);
}
export default assertNever;