Detect Collision

Detect-Collision.markdown

Detect Collision

In response to: http://stackoverflow.com/questions/29916874/can-you-tell-if-one-element-is-touching-another-using-javascript

A Pen by Gerald on CodePen.

License.

index.html

<div class="box" id="box1">1</div>
<div class="box" id="box2">2</div>
<div class="box" id="box3">3</div>
<div class="box" id="box4">4</div>

script.js

var boxes = document.querySelectorAll('.box');
for (var i = 0; i < boxes.length; i++) {
    if (boxes[i].addEventListener) {
        boxes[i].addEventListener('click', clickHandler);
    } else {
        boxes[i].attachEvent('onclick', clickHandler);
    }
}

var detectOverlap = (function () {
    function getPositions(elem) {
        var pos = elem.getBoundingClientRect();
        return [[pos.left, pos.right], [pos.top, pos.bottom]];
    }

    function comparePositions(p1, p2) {
        var r1, r2;
        r1 = p1[0] < p2[0] ? p1 : p2;
        r2 = p1[0] < p2[0] ? p2 : p1;
        return r1[1] > r2[0] || r1[0] === r2[0];
    }

    return function (a, b) {
        var pos1 = getPositions(a),
            pos2 = getPositions(b);
        return comparePositions(pos1[0], pos2[0]) && comparePositions(pos1[1], pos2[1]);
    };
})();

function clickHandler(e) {
    var elem     = e.target,
        elems    = document.querySelectorAll('.box'),
        elemList = Array.prototype.slice.call(elems),
        within   = elemList.indexOf(elem),
        touching = [];
    if (within !== -1) {
        elemList.splice(within, 1);
    }
    for (var i = 0; i < elemList.length; i++) {
        if (detectOverlap(elem, elemList[i])) {
            touching.push(elemList[i].id);
        }
    }
    if (touching.length) {
        alert(elem.id + ' touches ' + touching.join(' and ') + '.');
    } else {
        alert(elem.id + ' touches nothing.')   
    }

}

style.css

#box1 {
    background-color: LightSeaGreen;
}
#box2 {
    top: 25px;
    left: -25px;
    background-color: SandyBrown;
}
#box3 {
    left: -50px;
    background-color: SkyBlue;
}
#box4 {
    background-color: SlateGray;
}
.box {
    position: relative;
    display: inline-block;
    width: 100px;
    height: 100px;
    color: White;
    font: bold 72px sans-serif;
    line-height: 100px;
    text-align: center;
    cursor: pointer;
}
.box:hover {
    color: Black;
}