assertIsSignature

function assertIsSignature(
    putativeSignature,
): asserts putativeSignature is Signature;

import { assertIsSignature } from '@solana/keys';
 
// Imagine a function that asserts whether a user-supplied signature is valid or not.
function handleSubmit() {
    // We know only that what the user typed conforms to the `string` type.
    const signature: string = signatureInput.value;
    try {
        // If this type assertion function doesn't throw, then
        // Typescript will upcast `signature` to `Signature`.
        assertIsSignature(signature);
        // At this point, `signature` is a `Signature` that can be used with the RPC.
        const {
            value: [status],
        } = await rpc.getSignatureStatuses([signature]).send();
    } catch (e) {
        // `signature` turned out not to be a base58-encoded signature
    }
}