Frontend Refresh Project - An Electronic Spider

Preface: After learning JavaScript, you can use JavaScript to achieve some interesting effects. This article explains how to use JavaScript purely to implement an electronic spider on a web page.

Before we start learning how to write a web spider, let's take a look at what this electronic spider looks like:

You can see that it will move with our mouse, so how do you achieve this effect? ​​​​Let's start explaining.

HTML Code

    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Dreaming</title>
    <!-- External JavaScript files -->
    <script src=".test.js"></script>
    <style>
        /* Remove default padding and margins from body */
        body {
            margin: 0px;
            padding: 0px;
            position: fixed;
            /* Set the background color of webpage to black */
            background: rgb(0, 0, 0);
        }
    </style>



    <!-- Create a canvas for drawing -->
    <canvas id="canvas"></canvas>

As you can see our HTML code is very simple, let's start working on it!

Before you start writing JavaScript code, create a plan:

Overall process

• When the page loads, the canvas element and drawing context are initialized.

• Define tentacle objects . Each tentacle consists of multiple segments.

• Listen to mouse movement events and update the mouse position in real time.

• The tentacles are drawn through an animation loop, and they change dynamically according to the position of the mouse, creating a smooth animation effect.

The general process is the above steps, but I believe that you may not understand the above process before you have completed the writing of this code, but it doesn't matter anyways, so let's start writing our web spider:

Preface: In order to help you better understand the logic of the code, I have added comments to each code. I hope that you can understand the code bit by bit with the help of the comments:

JavaScript Code

// Define requestAnimFrame function
window.requestAnimFrame = function () {
    // Check if the browser supports requestAnimFrame function
    return (
        window.requestAnimationFrame ||
        window.webkitRequestAnimationFrame ||
        window.mozRequestAnimationFrame ||
        window.oRequestAnimationFrame ||
        window.msRequestAnimationFrame ||
        // If all these options are unavailable, use setTimeout to call the callback function
        function (callback) {
            window.setTimeout(callback)
        }
    )
}

// Initialization function to get canvas element and return related information
function init(elemid) {
    // Get canvas element
    let canvas = document.getElementById(elemid)
    // Get 2d drawing context, note that 'd' is lowercase
    c = canvas.getContext('2d')
    // Set canvas width to window inner width and height to window inner height
    w = (canvas.width = window.innerWidth)
    h = (canvas.height = window.innerHeight)
    // Set fill style to semi-transparent black
    c.fillStyle = "rgba(30,30,30,1)"
    // Fill the entire canvas with the fill style
    c.fillRect(0, 0, w, h)
    // Return drawing context and canvas element
    return { c: c, canvas: canvas }
}

// Execute function when page is fully loaded
window.onload = function () {
    // Get drawing context and canvas element
    let c = init("canvas").c,
        canvas = init("canvas").canvas,
        // Set canvas width to window inner width and height to window inner height
        w = (canvas.width = window.innerWidth),
        h = (canvas.height = window.innerHeight),
        // Initialize mouse object
        mouse = { x: false, y: false },
        last_mouse = {}

    // Function to calculate distance between two points
    function dist(p1x, p1y, p2x, p2y) {
        return Math.sqrt(Math.pow(p2x - p1x, 2) + Math.pow(p2y - p1y, 2))
    }

    // Define segment class
    class segment {
        // Constructor to initialize segment object
        constructor(parent, l, a, first) {
            // If it's the first tentacle segment, position is the tentacle top position
            // Otherwise, position is the nextPos coordinates of the previous segment object
            this.first = first
            if (first) {
                this.pos = {
                    x: parent.x,
                    y: parent.y,
                }
            } else {
                this.pos = {
                    x: parent.nextPos.x,
                    y: parent.nextPos.y,
                }
            }
            // Set segment length and angle
            this.l = l
            this.ang = a
            // Calculate coordinates for the next segment
            this.nextPos = {
                x: this.pos.x + this.l * Math.cos(this.ang),
                y: this.pos.y + this.l * Math.sin(this.ang),
            }
        }
        // Method to update segment position
        update(t) {
            // Calculate angle between segment and target point
            this.ang = Math.atan2(t.y - this.pos.y, t.x - this.pos.x)
            // Update position coordinates based on target point and angle
            this.pos.x = t.x + this.l * Math.cos(this.ang - Math.PI)
            this.pos.y = t.y + this.l * Math.sin(this.ang - Math.PI)
            // Update nextPos coordinates based on new position coordinates
            this.nextPos.x = this.pos.x + this.l * Math.cos(this.ang)
            this.nextPos.y = this.pos.y + this.l * Math.sin(this.ang)
        }
        // Method to return segment to initial position
        fallback(t) {
            // Set position coordinates to target point coordinates
            this.pos.x = t.x
            this.pos.y = t.y
            this.nextPos.x = this.pos.x + this.l * Math.cos(this.ang)
            this.nextPos.y = this.pos.y + this.l * Math.sin(this.ang)
        }
        show() {
            c.lineTo(this.nextPos.x, this.nextPos.y)
        }
    }

    // Define tentacle class
    class tentacle {
        // Constructor to initialize tentacle object
        constructor(x, y, l, n, a) {
            // Set tentacle top position coordinates
            this.x = x
            this.y = y
            // Set tentacle length
            this.l = l
            // Set number of tentacle segments
            this.n = n
            // Initialize tentacle target point object
            this.t = {}
            // Set random movement parameter for tentacle
            this.rand = Math.random()
            // Create first segment of the tentacle
            this.segments = [new segment(this, this.l / this.n, 0, true)]
            // Create other segments
            for (let i = 1; i = 0; i--) {
                this.segments[i].update(this.segments[i + 1].pos)
            }
            if (
                dist(this.x, this.y, target.x, target.y) 



<p>Here I roughly sort out the process of the above code:</p>

<p><strong>Initialization phase</strong></p>

• initFunction: When the page is loaded, the function init is called to get the canvas element and set its width and height to the size of the window. The obtained 2D drawing context is used for subsequent drawing.
• window.onload: After the page is loaded, initialize canvas and set context to the initial state of the mouse.

Definition of tentacle objects

• segmentClass: This is a segment of a tentacle. Each segment has a starting point (pos), length (l), angle (ang), and the position of the next segment is calculated by the angle ( nextPos).
• tentacleClass: Represents a complete tentacle, consisting of several segment. The starting point of the tentacle is at the center of the screen, and each tentacle contains multiple segments.

The main methods of tentacle are:
move: Update the position of each segment according to the mouse position.
show: Draw the path of the tentacle.

Event monitoring

• canvas.addEventListener('mousemove', ...): When the mouse moves, the mouse position is captured and stored in the mouse variable. Each mouse movement updates the coordinates of mouse and last_mouse for subsequent animations.

Animation loop

drawFunction : This is a recursive function used to create animation effects.

• First, it fills the canvas with a semi-transparent background in each frame, causing previously drawn content to gradually disappear, creating a smear effect.
• Then, iterate over all tentacles, calling their move and show methods, updating their positions and drawing each frame.
• Finally, use requestAnimFrame(draw) to make continuous recursive draw calls to form an animation loop.

Tentacle Behavior

• The movement of the tentacle move is implemented through the function. The last segment of the tentacle updates its position first, and then the other segments follow in sequence.
• The drawing of the tentacles is done through the show function, which iterates through all segments and draws lines, and finally displays them on the screen.

In this way, you have completed the production of the electronic spider!!!

Finally, let's take a look at the final effect:

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