Throb

Higher order functions to avoid race conditions, hammering, etc.

• debounce
• derace
• knock
• throttle
• turnstyle

debounce

Ensures a function is only executed if it has not been called again during some time.

Usage

In the example below, we search as the user types. We only want to make a network request if the user stops typing, so that there is not one request per keystroke.

import { debounce } from "@pomle/throb";

function search(query: string) {
  return fetch("http://search.com/query=" + query).then((result) => {
    console.log(result);
  });
}

const handleType = debounce(search, 500);

document.querySelector("#search").addEventListener("input", (event) => {
  handleType(event.target.value);
});

derace

Ensures that only the most up to date call to a resolved promise is used.

Usage

In the example below, we call a server to get the current time to display. If we did not use derace, an earlier call to getTime could resolve after the last, and show an outdated result. If an outdated promise resolves, the sync flag will be false, and the result can be ignored and the desync logged.

import { derace } from "@pomle/throb";

function getTime() {
  return fetch("http://time/now");
}

const updateTime = derace(getTime);

setInterval(() => {
  updateTime()
    .then(([time, sync]) => {
      if (sync) {
        window.title = time;
      } else {
        // Unsynced resolves may also be ignored or logged.
        throw new Error("Out of sync");
      }
    })
    .catch((error) => {
      console.info(error);
    });
}, 1000);

knock

Prevents calling function until it has been attempted to be called a number of times.

Usage

Example below shows an overlay when the user moves pointer over screen. In order to avoid being overly sensitive to movement, we ignore the 5 first events. We then forget that movement after 2000 ms of inactivity.

import { knock } from "@pomle/throb";

function handlePointer() {
  document.body.classList.add("overlay");
}

const threshold = 5;
const remember = 2000;

const onPointerMove = knock(handlePointer, threshold, remember);

window.addEventListener("pointermove", onPointerMove);

throttle

Ensures a function is executed exactly once per interval if called.

Usage

In the example below, we log the pointer position every time it is moved, and send to a server every half second at most.

import { throttle } from "@pomle/throb";

const buffer: number[] = [];

function flush() {
  const data = [...buffer];
  buffer.length = 0;

  return fetch("http://backend.com/data", {
    method: "POST",
    body: JSON.stringify(data),
  });
}

const readyToSend = throttle(flush, 500);

document.addEventListener("pointermove", (event) => {
  buffer.push(event.clientX);
  readyToSend();
});

turnstyle

Synchronously ensure only a single asynchronous call is in flight at any given time. Returns Promise if the call was allowed, otherwise undefined.

Usage

When saving data to a backend, you want to avoid multiple requests originating from user error. Accidentally clicking twice on a button could produce an error. Use turnstyle wrapper to ignore calls to a function while a Promise is in flight.

import { turnstyle } from "@pomle/throb";

function saveData(data: any) {
  return fetch("http://backend.com/data", {
    method: "POST",
    body: JSON.stringify(data),
  });
}

const saveSafe = turnstyle(saveData);

document.querySelector("button").addEventListener("click", (event) => {
  const promise = saveSafe({ name: "Turtles" });
  if (!promise) {
    alert("Take it easy");
    return;
  }

  promise
    .then(() => {
      alert("Data was saved");
    })
    .catch(() => {
      alert("Data saved failed");
    });
});