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I have a script that accesses a canvas element by id. It is based on this tutorial. He uses plain JavaScript and explains his method at about 5:10. I extrapolated to next.js below.

import React, { useEffect } from 'react';

export default function Simulator() {
    useEffect(() => {
        var canvas = document.getElementById("myCanvas");
        var c = canvas.getContext("2d");

        //deleted for simplicity, but similar code to his is below...
        
    }, [])
    
    return (
        <div className="mt-10">
            <canvas id="myCanvas" className="border-2"></canvas>
        </div>
    )
}

This fails without useEffect--I believe because document.getElementById is run before the element is rendered. I found several solutions, including making a custom hook, but useEffect appears to be the most elegant.

Is this how react is meant to be used? Is this my if "__name__" == "__main__" from Python but to guard against running on first render? Is the custom hook the preferred method? Thank you for your insights in advance.

giveearholdtongue
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1 Answers1

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Yes, useEffect is suitable for handling DOM interactions in functional React components as it allows to run side effects after rendering

You are correct, you try to access a canvas element by id, unavailable until the component is rendered. Using useEffect with an empty dependency array [], you tell React to run the effect once after initial rendering, similar to the componentDidMount lifecycle method in class components.

Using a custom hook is another way to abstract this logic, making the code modular and reusable. However, the custom hook would still need to use useEffect internally to handle the same issue.

In addition, you can use React's useRef to get a reference to the canvas element without accessing the DOM directly. Here's an example of how you can update your code:

import React, { useEffect, useRef } from 'react';

export default function Simulator() {
const canvasRef = useRef(null);

useEffect(() => {
    if (canvasRef.current) {
        const canvas = canvasRef.current;
        const c = canvas.getContext("2d");

        // rest of your code
    }
}, [])

return (
    <div className="mt-10">
        <canvas ref={canvasRef} className="border-2"></canvas>
    </div>)
}

This approach, using useRef, is more "React-like" as it avoids directly interacting with the DOM using document.getElementById, and instead relies on React's built-in functionality.

Daniel Soares
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