How to use CSS and D3 to implement a set of lanterns (with code)

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Source code download

https://github.com/comehope /front-end-daily-challenges

Code Interpretation

Define dom, the container contains 9 elements, representing 9 numbers:

<div>
    <span>3</span>
    <span>1</span>
    <span>4</span>
    <span>1</span>
    <span>5</span>
    <span>9</span>
    <span>2</span>
    <span>6</span>
    <span>5</span>
</div>

Centered display:

body {
    margin: 0;
    height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    background-color: black;
}

Define the container size:

.pi {
    width: 30em;
    height: 30em;
    font-size: 12px;
}

Lay out 9 numbers into a 3 * 3 grid:

.pi {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    grid-gap: 0.2em;
}

.pi span {
    color: white;
    font-size: 3em;
    background-color: hsl(0, 40%, 40%);
    font-family: sans-serif;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    user-select: none;
}

Define the css variable in the dom, and the variable value is equal to the number represented by the element :

<p>
    <span>3</span>
    <span>1</span>
    <span>4</span>
    <span>1</span>
    <span>5</span>
    <span>9</span>
    <span>2</span>
    <span>6</span>
    <span>5</span>
</p>

Set different background colors for different numbers:

.pi span {
    --c: hsl(calc(var(--d) * 36), 40%, 40%);
    background-color: var(--c);
}

Make the numbers the same color as the background, and on mouseover, height the current number:

.pi span {
    color: var(--c);
    transition: 0.3s;
}

.pi span:hover {
    background-color: white;
    color: black;
    box-shadow: 0 0 1em yellow;
}

At this point, the visual effect design is completed, and then d3 is used to batch process dom elements and css variables.
Introduce the d3 library:

<script></script>

Delete the dom element representing the number in the html file, use d3 to create the dom element representing the number, and set the css variable:

const PI = '314159265';

d3.select('.pi')
    .selectAll('span')
    .data(PI)
    .enter()
    .append('span')
    .style('--d', (d) => d)
    .text((d) => d);

Put PI Change to 100 digits:

const PI = '3141592653589793238462643383279502884197169399375105820974944592307816406286208998628034825342117067';

At the same time, change the grid to a 10 * 10 layout:

.pi {
    grid-template-columns: repeat(10, 1fr);
}

.pi span {
    font-size: 1.3em;
}

Next, create a loop lighting effect.

Add css classes for each number element. The class name of number 0 is d0, the class name of number 1 is d2, and so on:

d3.select('.pi')
    .selectAll('span')
    .data(PI)
    .enter()
    .append('span')
    .attr('class', (d) => `d${d}`)
    .style('--d', (d) => d)
    .text((d) => d);

Define a loop variable number, which starts from 1 and gradually increments:

let number = 1;

Define a function that lights up a set of elements with a specific number:

function show() {
    d3.selectAll(`.pi span.d${number % 10}`)
        .classed('show', true);
    d3.selectAll(`.pi span.d${(number-1) % 10}`)
        .classed('show', false);
    number++;
}

Finally, set an interval and call the above function repeatedly to let each group of numbers light up in sequence:

setInterval(show, 500);

You’re done!

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