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JavaScript

Posted by Conor Vanoystaeyen
Conor Vanoystaeyen
16,687 Points

Can't figure out these codes

I found this code on codepen but don't understand how it works. It also says js (babel) isn't this normal js?

Codepen link → https://codepen.io/electerious/pen/MQrRxX

document.querySelector('.button').onmousemove = (e) => {

    const x = e.pageX - e.target.offsetLeft
    const y = e.pageY - e.target.offsetTop

    e.target.style.setProperty('--x', `${ x }px`)
    e.target.style.setProperty('--y', `${ y }px`)

}

1 Answer

Blake Larson
Blake Larson
13,014 Points
Blake Larson
Blake Larson
13,014 Points

The x and y javascript variables are finding the absolute position of where the mouse is on the button element. You can log them as you hover on the button..

document.querySelector('.button').onmousemove = (e) => {

    console.log({
        left: e.pageX - e.target.offsetLeft,
        top: e.pageY - e.target.offsetTop
    });
    const x = e.pageX - e.target.offsetLeft
    const y = e.pageY - e.target.offsetTop
// setProperty sets the --x and --y variable in the scss file..
// to the x and y variable which changes
// the absolute top and and left position of the ::before element
//  that is 0px height and width initially, 
// but changes to a height and width 400px
// when there is a hover on the button (&:hover::before { --size: 400px;} 
// so the ::before element changes position
    e.target.style.setProperty('--x', `${ x }px`) 
    e.target.style.setProperty('--y', `${ y }px`)
}

Also, if you take the overflow: hidden; style off of the .button you can see the blur follow the mouse around and wrap your head around the trick a little easier.