function is<T extends string>(value: string, prefix: T): value is `${typeof prefix}_${string}` {
      return value.startsWith(`${prefix}_`)
    }

You can now do `is(id, 'user')`.

If you do that often you probably want to create separate functions, e.g.:

    function isFactory<T extends string>(prefix: T) {
      return (value: string) => is(value, prefix)
    }

    const isUser = isFactory('user')
    const isOrder = isFactory('order')

Not too bad.