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 typesin the union
// Will throw an Error whencalled at runtime.
// Use `assertNever(arg, true)` insteadto fail silently.
return assertNever(arg);
Helper function for exhaustive checks of discriminated unions. https://basarat.gitbooks.io/typescript/docs/types/discriminated-unions.html
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);}