Getting elements from selected area in Javascript

Question

I need to implement getting elements from selected area in Javascript. This is needed to make a better, desktop-like UI in chrome app. The nearest example is selecting area in Imgur extension:

So the question is:

1. How this selecting can be done in javascript?
2. How to get elements from this selection?

Answer 1

I found this interesting so I made something from scratch, using jQuery because it would become too complicated otherwise: http://jsfiddle.net/EuSBU/1/.

I hope it's straight-forward enough to follow, please ask if there is something you want to know.

It basically comes down to checking for each element whether the rectangle is encapsulating it.

$("#start_select").click(function() {
    $("#select_canvas").show();
});

$('*').bind('selectstart', false);

var start = null;
var ctx = $("#select_canvas").get(0).getContext('2d');
ctx.globalAlpha = 0.5;

$("#select_canvas").mousedown(function(e) {
    start = [e.offsetX, e.offsetY];

}).mouseup(function(e) {
    end = [e.offsetX, e.offsetY];

    var x1 = Math.min(start[0], end[0]),
        x2 = Math.max(start[0], end[0]),
        y1 = Math.min(start[1], end[1]),
        y2 = Math.max(start[1], end[1]);

    var grabbed = [];
    $('*').each(function() {
        if(!$(this).is(":visible")) return;

        var o = $(this).offset(),
            x = o.left,
            y = o.top,
            w = $(this).width(),
            h = $(this).height();

        if(x > x1 && x + w < x2 && y > y1 && y + h < y2) {
            grabbed.push(this);
        }
    });
    console.log(grabbed);

    start = null;

    $(this).hide();

}).mousemove(function(e) {
    if(!start) return;

    ctx.clearRect(0, 0, this.offsetWidth, this.offsetHeight);
    ctx.beginPath();

    var x = e.offsetX,
        y = e.offsetY;

    ctx.rect(start[0], start[1], x - start[0], y - start[1]);
    ctx.fill();
});