Move html element using JavaScript across page

Question

I am working with JavaScript to move an HTML div across the page. Below is the movement that I want the element to follow:

It should be starting and following routes 1, 2, 3 and 4. It should only change the route once the element reaches the max width/height of the page. I am using the below code and I am stuck on how to continue further.

var box = document.getElementById("box");
var height = document.getElementById("container").offsetHeight;
var widht = document.getElementById("container").offsetWidth;

window.setInterval(() => {
    let addPosition = (parseInt(box.style.top) + 10);
    let subPosition = (parseInt(box.style.top) - 10);

    if (addPosition > height)
        box.style.top = subPosition + 'px';
    else
        box.style.top = addPosition + 'px';
}, 100);

#container {
   position: absolute;
   background: purple;
   width: 100%;
   height: 100%;
}

#box {
   position: absolute;
   background: red;
   width: 30px;
   height: 30px;
}

<div id="container">
    <div id="box" style="top: 0px; left: 0px;"></div>
</div>

why not use CSS animation?

tacoshy
– tacoshy

2022-07-31 19:31:08 +00:00
Commented Jul 31, 2022 at 19:31 — tacoshy
– tacoshy, Commented Jul 31, 2022 at 19:31
@tacoshy - Can you help me with the code?

HarshSharma
– HarshSharma

2022-07-31 19:32:16 +00:00
Commented Jul 31, 2022 at 19:32 — HarshSharma
– HarshSharma, Commented Jul 31, 2022 at 19:32

tacoshy · Accepted Answer · 2022-07-31 19:44:39Z

3

No JS is needed to make this animation. You can use CSS-Animations for this.

For that, you use keyframes and change the position where the element should move to. You can define the speed with the animation-duration property and repeat it with animation-iteration-count

body {
  margin: 0;
  height: 100vh;
}

div {
  height: 50px;
  width: 50px;
  background-color: red;
  position: fixed;
  animation-name: moveBox;
  animation-duration: 5s;
  animation-iteration-count: infinite;
}

@keyframes moveBox {
  0% { top: 0; left: 0; }
  20% { top: calc(100% - 50px); left: 0; }
  50% { top: 0; left: calc(100% - 50px); }
  70% { top: calc(100% - 50px); left: calc(100% - 50px); }
  100% { top: 0; left: 0; }
}

<div></div>

answered Jul 31, 2022 at 19:44

tacoshy

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Comments

Orteil · Accepted Answer · 2022-07-31 19:43:36Z

As someone else mentioned, this is normally done with CSS animations, but if you have to use javascript you basically want a state system that keeps track of what your current target is.

Here's roughly how you could do it:

    let box = document.getElementById("box");
    let height = document.getElementById("container").offsetHeight;
    let width = document.getElementById("container").offsetWidth;
    
    let getAngle=function(x1,y1,x2,y2)
    {
      return Math.atan2(y2-y1,x2-x1);
    }
    
    let state=0;
    let speed=10;//how many pixels to move per interval
    let x=0,y=0;
    let xTarget=0,yTarget=0;
    
    window.setInterval(() => {
        
        //we do not account for the box's size here, but if we needed to we could add or subtract it to the target as needed
        switch(state) {
          case 0:
            xTarget=0;
            yTarget=height;
            break;
          case 1:
            xTarget=width;
            yTarget=0;
            break;
          case 2:
            xTarget=width;
            yTarget=height;
            break;
          case 3:
            xTarget=0;
            yTarget=0;
            break;
        }
        
        //do we still have more steps left? calculate the angle to the target, then step in that direction
        if (state<4)
        {
          var angle=-getAngle(x,y,xTarget,yTarget)+Math.PI/2;
          x+=Math.sin(angle)*speed;
          y+=Math.cos(angle)*speed;
        }
        
        //are we close enough to the target? snap to the target, then switch to the next state
        //note: you may want to calculate the actual distance here instead
        if (Math.abs(xTarget-x)<speed && Math.abs(yTarget-y)<speed)
        {
            x=xTarget;
            y=yTarget;
            state++;
        }
        
        if (state>=4) state=0;//if you want the movement to loop
        
        box.style.left=x+'px';
        box.style.top=y+'px';
    }, 100);

#container {
   position: absolute;
   background: purple;
   width: 300px;
   height: 200px;
}

#box {
   position: absolute;
   background: red;
   width: 30px;
   height: 30px;
}

<div id="container">
    <div id="box" style="top: 0px; left: 0px;"></div>
</div>

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