42 lines
1.2 KiB
JavaScript
42 lines
1.2 KiB
JavaScript
|
"use strict";
|
||
|
|
Object.defineProperty(exports, "__esModule", { value: true });
|
||
|
|
exports.assertNever = assertNever;
|
||
|
|
/**
|
||
|
|
* 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);
|
||
|
|
* }
|
||
|
|
*/
|
||
|
|
function assertNever(value, errorMessageOrNoThrow) {
|
||
|
|
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: ".concat(JSON.stringify(value)));
|
||
|
|
}
|
||
|
|
exports.default = assertNever;
|