Polling

waitFor(fn, options)

Wait for the callback to execute successfully. If the callback throws an error or returns a rejected promise, it will continue to wait until it succeeds or times out.

This is useful when you need to wait for some asynchronous action to complete, for example, when a server is starting up.

import { waitFor } from "mix-n-matchers/utilities";

const server = { isReady: false };

setTimeout(() => {
server.isReady = true;
}, 100);

await waitFor(
() => {
if (!server.isReady) {
throw new Error("Server not started");
}
},
{
timeout: 500,
interval: 20,
},
);

expect(server.isReady).toBe(true);

Tests

waitUntil(fn, options)

This is similar to waitFor, but if the callback throws any errors, execution is immediately interrupted and an error message is received. If the callback returns a falsy value, the next check will continue until a truthy value is returned.

This is useful when you need to wait for something to exist before taking the next step.

import { waitUntil } from "mix-n-matchers/utilities";

const element = await waitUntil(
() => document.querySelector(".element"),
{
timeout: 500,
interval: 20,
},
);

expect(element?.querySelector(".element-child")).toBeTruthy();

Tests