赤いセロファンっぽいもの - jsdo.it - Share JavaScript, HTML5 and CSSvar front = document.getElementById('front'); var back = document.getElementById('back'); var drag = null; front.addEventListener('mousedown', function(ev) { var rect = back.getBoundingClientRect(); var x = ev.pageX, y = ev.pageY; if (rect.left <= x && x < rect.right && rect.top <= y && y < rect.bottom) { drag = [rect.left - x, rect.top - y]; ev.preventDefault(); } }, false); back.addEventListener
