React Hooks: useSlider | Joel M Turner

Creating a slider with React hooks that slides through an array on an interval.

We had a need for an auto advancing image slider in React. I chose to use hooks for this feature. This hook leverages a useInterval hook from Dan Abrimov.

What We’re Building TL;DR

Requirements

This component needs do a few things.

Should accept an slide array
Should accept a duration in milliseconds
Should animate between slides
Should move through array on it’s own

useInterval

Here’s the useInterval code.

import React, { useState, useEffect, useRef } from "react";

function useInterval(callback, delay) {
  const savedCallback = useRef();

  // Remember the latest callback.
  useEffect(() => {
    savedCallback.current = callback;
  }, [callback]);

  // Set up the interval.
  useEffect(() => {
    function tick() {
      savedCallback.current();
    }
    if (delay !== null) {
      let id = setInterval(tick, delay);
      return () => clearInterval(id);
    }
  }, [delay]);
}

Setting an interval can be problematic in JavaScript, mostly because of cleanup (or lack of). With useEffect we get a nice cleanup with the return function, return () => clearInterval(id);.

useSlider

Now that we have that set up we can leverage it to help us with timing.

import * as React from "react";
import useInterval from "./UseInterval";

function useSlider({
  total = 0, // the length of the slide array
  enabled = false, // pauses/disables the player
  useLoaded = false, // this allows for delayed loads like images or embeds
  speed = 1000, // speed in milliseconds to show each slide
  loop = true, // should it start back at the beginning
}) {
  const [offset, setOffset] = React.useState(0);
  const [items, setItems] = React.useState([]);

  function incrementOffset() {
    if (offset === total - 1) {
      setOffset(loop ? 0 : offset);
    } else {
      setOffset(offset + 1);
    }
  }

  function addItem(ref) {
    setItems([...items, ref]);
  }

  const loaded = useLoaded ? items.length === total : true;

  useInterval(() => {
    if (loaded && enabled && offset < total) {
      incrementOffset();
    }
  }, speed);

  return {
    offset, // this is the current index of the slider
    addItem, // this takes a ref and adds it to the items array to see if all have loaded
  };
}

export default useSlider;

Slider Component

Our slider component adds all slides next to each other and moves the .scroller (absolutely positioned) through the .container (relatively positioned). This allows us to animate between the slides. Here’s the stateless structure of our component.

.container {
  background-color: #ccc;
  margin: 0 auto;
  position: relative;
  overflow: hidden;
}

.scroller {
  position: absolute;
  transition: transform 350ms;
  height: 100%;
  display: flex;
}

.slide {
  display: flex;
  align-items: center;
  justify-content: center;
  position: relative;
  transition: opacity 350ms;
}

import React from "react";
import useSlider from "./useSlider";

const slides = [
  {
    title: "Slide 1",
    color: "#56777A",
  },
  {
    title: "Slide 2",
    color: "#84ACAC",
  },
  {
    title: "Slide 3",
    color: "#FBA434",
  },
];

function Slider() {
  const slideWidth = 300;

  return (
    <div
      className="container"
      style={{
        backgroundColor: slide.color,
        width: slideWidth,
        height: slideWidth,
      }}
    >
      <div
        className="scroller"
        style={{
          // our counter offset will go here
          transform: `translate3d(-${offset * slideWidth}px,0,0)`,
          width: `${slides.length * slideWidth}px`,
        }}
      >
        {slides.map((slide, index) => (
          <div
            key={slide.title}
            className="slide"
            style={{
              backgroundColor: slide.color,
              width: slideWidth,
              height: slideWidth,
            }}
          >
            {slide.title}
          </div>
        ))}
      </div>
    </div>
  );
}

Putting it All Together

Now we can add our hook to our slider component. This will give us all the state that we’ll need for this feature. When it’s all together we get a slider that moves the slides horizontally and rewinds after the last one. You can hook up the slider props to manage the slider options if needed. It can also be made to go vertical with a little modification.

Cool! Requirements met.

Should accept an slide array
Should accept a duration in milliseconds
Should animate between slides
Should move through array on it’s own