I have a 16x16 grid of small squares. I have added a permanent "hover" effect to make the very first box turn red when I put my mouse over it. However, I want to add the same effect to all of the boxes on the page. I can't figure out how to do it - I have tried to add an event listener to the whole page and used target.nodeName and target.NodeValue, but to no avail. I have included the working version where the fix box turns red on mouseover.

var n=16; //take grid column value as you want

const bigContainer = document.querySelector('.bigContainer')

for(var i = 1; i < n; i++) {
    bigContainer.innerHTML+='<div class="row">';

    for(j = 0; j < n; j++) {
        bigContainer.innerHTML+='<div class="smallBox">';
    }
}

const smallBox = document.querySelector('.smallBox');

smallBox.addEventListener('mouseover', () => {
    smallBox.classList.add('permahover');
});

.smallBox {
    border: 1px solid black;
    width: 20px;
    height: 20px;
    display: inline-block;
}

.permahover {
    background: red;
}

h1 {
    text-align: center;
}

.bigContainer {
    text-align: center;
}

<h1>Etch-a-Sketch Assignment - The Odin Project</h1>
<div class="bigContainer">

</div>

I have a 16x16 grid of small squares. I have added a permanent "hover" effect to make the very first box turn red when I put my mouse over it. However, I want to add the same effect to all of the boxes on the page. I can't figure out how to do it - I have tried to add an event listener to the whole page and used target.nodeName and target.NodeValue, but to no avail. I have included the working version where the fix box turns red on mouseover.

var n=16; //take grid column value as you want

const bigContainer = document.querySelector('.bigContainer')

for(var i = 1; i < n; i++) {
    bigContainer.innerHTML+='<div class="row">';

    for(j = 0; j < n; j++) {
        bigContainer.innerHTML+='<div class="smallBox">';
    }
}

const smallBox = document.querySelector('.smallBox');

smallBox.addEventListener('mouseover', () => {
    smallBox.classList.add('permahover');
});

.smallBox {
    border: 1px solid black;
    width: 20px;
    height: 20px;
    display: inline-block;
}

.permahover {
    background: red;
}

h1 {
    text-align: center;
}

.bigContainer {
    text-align: center;
}

<h1>Etch-a-Sketch Assignment - The Odin Project</h1>
<div class="bigContainer">

</div>

• javascript
• html
• css

• 1 @StephenP not OP, but I'd imagine OP wants the hover state to persist , as the html is titled "Etch-a-Sketch Assignment" – Damon Commented Mar 20, 2020 at 21:05

6 Answers 6

The immediate problem you are having is that this is only querying, and subsequently adding an event listener to, one element.

const smallBox = document.querySelector('.smallBox');

smallBox.addEventListener('mouseover', () => {
    smallBox.classList.add('permahover');
});

In the above portion of your code, querySelector only returns the first matching element. You may be looking for querySelectorAll here which returns a NodeList of matching elements.

You have two options (perhaps others if you want to restructure your code further). The naive approach is to, in fact, query for all of the cells and add event listeners to each of them.

var n=16; //take grid column value as you want

const bigContainer = document.querySelector('.bigContainer')

for(var i = 1; i < n; i++) {
    bigContainer.innerHTML+='<div class="row">';

    for(j = 0; j < n; j++) {
        bigContainer.innerHTML+='<div class="smallBox">';
    }
}

const smallBoxes = document.querySelectorAll('.smallBox');

[...smallBoxes].forEach(smallBox => {
  smallBox.addEventListener('mouseover', () => {
      smallBox.classList.add('permahover');
  });
})

.smallBox {
    border: 1px solid black;
    width: 20px;
    height: 20px;
    display: inline-block;
}

.permahover {
    background: red;
}

h1 {
    text-align: center;
}

.bigContainer {
    text-align: center;
}

<h1>Etch-a-Sketch Assignment - The Odin Project</h1>
<div class="bigContainer">

</div>

Another option is to use event delegation as you identified. Here is how you can leverage that. Note: this approach is a bit tricker for an aggressive event like "mouseover" as you may get false positive targets (like the outer container for example).

var n=16; //take grid column value as you want

const bigContainer = document.querySelector('.bigContainer')

for(var i = 1; i < n; i++) {
    bigContainer.innerHTML+='<div class="row">';

    for(j = 0; j < n; j++) {
        bigContainer.innerHTML+='<div class="smallBox">';
    }
}

bigContainer.addEventListener('mouseover', e => {
  var target = e.target

  if (target !== bigContainer) {
    target.classList.add('permahover')
  }
})

.smallBox {
    border: 1px solid black;
    width: 20px;
    height: 20px;
    display: inline-block;
}

.permahover {
    background: red;
}

h1 {
    text-align: center;
}

.bigContainer {
    text-align: center;
}

<h1>Etch-a-Sketch Assignment - The Odin Project</h1>
<div class="bigContainer">

</div>

You need to use a delegation event, because all the small boxes don't exist on the page when the page is loaded (You can figure out in the inspector element that only your first box has the event listener).

So you listen the whole container (because it is always on the page on load)

bigContainer.addEventListener('mouseover', () => {
    // Code for checking if we hovered a small div & if yes applying the style
});

...and then do a paraison with the event.target (which will be the small div hovered)

if (event.target.matches('.smallBox')) {
    event.target.classList.add('permahover');
}

var n=16; //take grid column value as you want

const bigContainer = document.querySelector('.bigContainer')

for(var i = 1; i < n; i++) {
    bigContainer.innerHTML+='<div class="row">';

    for(j = 0; j < n; j++) {
        bigContainer.innerHTML+='<div class="smallBox">';
    }
}

const smallBox = document.querySelector('.smallBox');

bigContainer.addEventListener('mouseover', () => {
    if (event.target.matches('.smallBox')) {
        event.target.classList.add('permahover');
    }
});

.smallBox {
    border: 1px solid black;
    width: 20px;
    height: 20px;
    display: inline-block;
}

.permahover {
    background: red;
}

h1 {
    text-align: center;
}

.bigContainer {
    text-align: center;
}

<h1>Etch-a-Sketch Assignment - The Odin Project</h1>
<div class="bigContainer">

</div>

You can use forEach method to loop through all boxes and add eventListener on each one. If all of them have .smallBox class you can do it like this:

const smallBoxes = document.querySelectorAll('.smallBox');

smallBoxes.forEach(box => box.addEventListener('mouseover', () => {
    smallBox.classList.add('permahover');
}))

I hope it helped you!

let smallBoxes = document.querySelectorAll('.smallBox');
[...smallBoxes].forEach(el => {
    el.addEventListener('mouseover', e => e.target.classList.add('permahover'));
});

you should set the eventlistener to your DOM and ask if the trigger element are one of your elements which are that specific class. So you can handle every element with that class.

var n = 16; //take grid column value as you want

const bigContainer = document.querySelector('.bigContainer')

for (var i = 1; i < n; i++) {
  bigContainer.innerHTML += '<div class="row">';

  for (j = 0; j < n; j++) {
    bigContainer.innerHTML += '<div class="smallBox">';
  }
}

document.addEventListener('mouseover', function(e) {
  if (e.target && e.target.className == 'smallBox') {
        var target = e.target;
        target.classList.add('permahover');
  }
});

Working js fiddle: https://jsfiddle/nwukf205/

hope i could help you :) if you got questions just ask

Have you tried the :hover selector? Not sure if you want specify any dynamic actions here, but it's easy to do basic stuff.

https://www.w3schools./cssref/sel_hover.asp

a:hover {
   background-color: yellow;
 }

I haven't tried your example myself but something similar to this has been answered here:

Hover on element and highlight all elements with the same class