var wrapper = document.getElementById("signature-pad"), // clearButton = wrapper.querySelector("[data-action=clear]"), saveDataButton = wrapper.querySelector("[data-action=save-data]"), canvas = wrapper.querySelector("canvas"), signaturePad; // Adjust canvas coordinate space taking into account pixel ratio, // to make it look crisp on mobile devices. // This also causes canvas to be cleared. function resizeCanvas() { // When zoomed out to less than 100%, for some very strange reason, // some browsers report devicePixelRatio as less than 1 // and only part of the canvas is cleared then. var ratio = Math.max(window.devicePixelRatio || 1, 1); canvas.width = canvas.offsetWidth * ratio; canvas.height = canvas.offsetHeight * ratio; canvas.getContext("2d").scale(ratio, ratio); } window.onresize = resizeCanvas; resizeCanvas(); signaturePad = new SignaturePad(canvas); document.getElementById('clear').addEventListener('click', function() { signaturePad.clear(); }); saveDataButton.addEventListener("click", function (event) { if (signaturePad.isEmpty()) { alert("Por favor firme primero."); } else { saveViaAJAX(); } });