AngularJs Virtual Repeater with a Grid

So I had a grid of images I displayed with an Angular ng-repeat, where the number of images was in the hundreds. This was just killing performance and overloading the DOM. I was getting super frustrated with the choppy scrolling and overall slow loading.

It occurred to me to use a virtual repeater, however, they either support vertical or horizontally stacked elements, not a grid. In order to get this to work, I need to structure my elements in a 2D array. That way I could still use the repeater on spitting out rows of image arrays and gain a performance boost through that.

2D Structure:
[img, img, img, img] ,
[img, img, img, img] ,
[img, img, img, img] ,
[img, img, img, img]

img = the image source url

The first thing I did, was make sure I knew the width of the total space for the grid and width of each element. I want to make sure I fill the space, so I did the math to know how many elements will fill the total space and that will be my column count. I recommend to setup some listeners on the grid width to catch changes from the user changing the window size, I won’t be showing that part in this example. The snippet below shows the creation of my 2D array that will be fed to the repeater.

//Passing in my array of images that I need to break down into a 2D array
//Also, including the width of the entire grid space and each image's uniformed width
function computeRows(imageArray, width, imageWidth) {
    var rows = [];
    if (imageArray) {
        const rowCount = width/ imageWidth;
        const copy = imageArray.slice(); //using a copy instead of affecting actual element
        while (copy.length) { //create the 2D array by looping through the imageArray and splicing it into chunks
            rows.push(copy.splice(0, rowCount)); 
    return rows;
//Will need to bind computeRows() to the scope

Once I have my 2D array, I bound it to me scope and used it in my template. I chose to use vs-repeat because it was very quick and easy to implement.

<div vs-repeat vs-excess="10">
    <div ng-repeat="row in rows">
            ng-repeat="img in row"

That was it, the end result was awesome, vs-repeat handled just showing what was necessary for the user experience and loading the remainder DOM elements as the user scrolled through the grid.

Javascript Cloning and Moving DOM Elements to Mouse Position

So I was working with dragula, a super easy to use drag and drop library. However, I ran into an issue where when a user clicks the dragging element, I wanted everything in the background to collapse. This messed up the dragging element’s position in relation to where the mouse’s location. In most cases when you drag and drop an element, it hovers wherever your mouse is located. In my case, when I shifted everything, the element I wanted to drag was no longer located where I clicked but rather it moved and hovered in the wrong spot with the wrong offset from my mouse. In using this library, I didn’t have access to changing their inner coding offset logic, so I needed to come up with my own fix. In the end, I decided to hide their floating mouse DOM element and create my own, that I had control over. The following code shows how to do just that!

Happy coding! Let me know if you have any comments or improvements.

//call this function when we want to initiate the listener for moving the mouse
//For instance, call this function once the user starts dragging an element
//requires an event and element to be passed.
function startMouseMove(e, element) {
    $('.my-background-content').css( 'display', 'none' ); //collapse background elements
    const container = $(element).find('.item-to-clone').clone().appendTo('.my-container'); //clone the element you want to hover around mouse
    $(container).attr('id', 'cursor_element'); //give the clone element an id so we can reference it later
    $('#cursor_element').css({'position': 'fixed', 'top': e.pageY, 'left': e.pageX}); //set clone element's position to mouse's position
    $document.on('mousemove', moveElement); //bind mouse event
function moveElement(e) {
    const y = e.pageY; //get y position
    const x = e.pageX; //get x position
    $('#cursor_element').css({'top': y, 'left': x}); //move the position of the element to match mouse, whenever mouse moves
//call this function when we want to stop the listener for moving the mouse
//For instance, call this function once the user drops a dragging element
function stopMouseMove() {
    $('#cursor_element').remove(); //delete cloned element
    $('.my-background-content').css( 'display', '' ); //un-collapse background elements
    $document.unbind('mousemove', moveElement); //unbind mouse event

Note that $document and JQuery must be declared/injected into the controller for this to work.

The above code requires JQuery, but you could easily use vanilla Javascript. Check this out for event help and this out for DOM selection.