localstorage

[jesesqui]

I'm trying to do an autosave with localstorage and it works assigning the key and the value like this:
var pdf = new PDFAnnotate("pdf-container", "my_document.pdf", {
onPageUpdated(page, oldData, newData) {
localStorage.setItem(page, JSON.stringify(newData));
console.log("page "+ page, oldData, newData);
},
and then with a button to load the localstoage but this last one without success, could you guide me on how to achieve this

var canvas = document.getElementById('pdf-container'),
document.getElementById("btnLoad").onclick = function () {
var idt = localStorage.getItem(1) || null;
if (idt !== null) {
var data = JSON.parse(idt);
canvas.putImageData(idt, 0, 0);
}