How to check if a given value is in a union type array

Question

I have an array of given union type, then wants to check if a string from a superset of the union type is contained in the array (runtime check):

Answer 1

The accepted answer uses type assertions/casting but from the comments it appears the OP went with a solution using find that works differently. I prefer that solution also, so here's how that can work:

const configKeys = ['foo', 'bar'] as const;
type ConfigKey = typeof configKeys[number]; // "foo" | "bar"

// Return a typed ConfigKey from a string read at runtime (or throw if invalid).
function getTypedConfigKey(maybeConfigKey: string): ConfigKey {
    const configKey = configKeys.find((validKey) => validKey === maybeConfigKey);
    if (configKey) {
        return configKey;
    }
    throw new Error(`String "${maybeConfigKey}" is not a valid config key.`);
}

Note that this can guarantee that a string is a valid ConfigKey both at runtime and compile time.