Implement a JavaScript API for document scanning

chrome/common/extensions/docs/examples/api/document_scan/scan.js

+var requestButton = document.getElementById("requestButton");
+var listScanners = document.getElementById('listScanners');
+var scanButton = document.getElementById('scanButton');
+var scanOption = document.getElementById('scanOption');
+var scanModes = [
+    document.getElementById('scanModeColor'),
+    document.getElementById('scanModeGrey'),
+    document.getElementById('scanModeBW')
+  ];
+var scannerName = document.getElementById('scannerName');
+var scannedImages = document.getElementById('scannedImages');
+var waitAnimation = document.getElementById('waitAnimation');
+var scanner;
+var imageMimeType;
+
+function setOnlyChild(parent, child) {
+  while (parent.firstChild) {
+    parent.removeChild(parent.firstChild);
+  }
+  parent.appendChild(child);
+}
+
+var gotScannerList = function(scanners) {
+  waitAnimation.style.display = 'none';
+  console.log('Got ' + scanners.length + ' scanners');
+  if (scanners.length > 0) {
+    scanOption.style.display = 'block';
+    scanner = scanners[0].name;
+    imageMimeType = scanners[0].imageMimeType;
+    console.log('Using scanner ' + scanner);
+    setOnlyChild(scannerName, document.createTextNode(scanner));
+  } else {
+    scanOption.style.display = 'none';
+  }
+};
+
+var gotPermission = function(result) {
+  waitAnimation.style.display = 'block';
+  requestButton.style.display = 'none';
+  listScanners.style.display = 'block';
+  console.log('App was granted the "documentScan" permission.');
+  chrome.documentScan.listScanners(gotScannerList);
+};
+
+var permissionObj = {permissions: ['documentScan']};
+
+requestButton.addEventListener('click', function() {
+  waitAnimation.style.display = 'block';
+  chrome.permissions.request( permissionObj, function(result) {
+    if (result) {
+      gotPermission();
+    } else {
+      console.log('App was not granted the "documentScan" permission.');
+      console.log(chrome.runtime.lastError);
+    }
+  });
+});
+
+listScanners.addEventListener('click', function() {
+  waitAnimation.style.display = 'block';
+  chrome.documentScan.listScanners(gotScannerList);
+});
+
+function getPngDataUrl(buffer) {
+  // Much discussion on the relative performance of various methods for doing
+  // this conversion at http://jsperf.com/encoding-xhr-image-data/16 and
+  // https://gist.github.com/jonleighton/958841.  Picking the most concise
+  // version that works.
+  console.log('Making bytes from buffer');
+  var bytes = new Uint8Array(buffer);
+  var len = bytes.byteLength;
+  console.log('Making binary from bytes');
+  var binary = '';
+    for (var i = 0; i < len; i++) {
+    binary += String.fromCharCode(bytes[i]);
+  }
+  console.log('Returning btoa');
+  return 'data:' + imageMimeType + ';base64,' + btoa(binary);
+}
+
+var onScanCompleted = function(buffer) {
+  waitAnimation.style.display = 'none';
+  if (chrome.runtime.lastError) {
+    console.log('Scan failed: ' + chrome.runtime.lastError.message);
+    return;
+  }
+  console.log('Scan completed with data length ' +
+              buffer.byteLength + '.');
+  console.log(buffer);
+  urlData = getPngDataUrl(buffer);
+  console.log('URL is ' + urlData);
+  var scannedImage = document.createElement('img');
+  scannedImage.src = urlData;
+  scannedImages.insertBefore(scannedImage, scannedImages.firstChild);
+};
+
+scanButton.addEventListener('click', function() {
+  var scanProperties = {};
+  for (var idx = 0; idx < scanModes.length; ++idx) {
+    if (scanModes[idx].checked) {
+      var scanMode = scanModes[idx].value;
+      console.log('Scanning type is ' + scanMode);
+      scanProperties['mode'] = scanMode;
+      break;
+    }
+  }
+  waitAnimation.style.display = 'block';
+  chrome.documentScan.scan(scanner, scanProperties, onScanCompleted);
+});
+
+chrome.permissions.contains(permissionObj, function(result) {
+  if (result) {
+    gotPermission();
+  }
+});