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Created November 29, 2022 05:42
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const values = ['foo', 'bar'] as const;
type MyValues = typeof values[number];
function isOneOfMyValues(elem: unknown): elem is MyValues {
const opts: string[] = [...values];
return opts.includes(String(elem));
function lengthOfMyThing(x: MyValues | null) {
if (isOneOfMyValues(x)) {
return x.length;
return 0;
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