Create a mechanism for generating a random id

This will be used to give each template a unique, serializable id.

Author: Godhuda

packages/htmlbars-compiler/lib/utils.js

@@ -1,3 +1,6 @@
+/*globals window:false*/
+/*globals Uint8Array:false*/
+
 export function processOpcodes(compiler, opcodes) {
   for (var i=0, l=opcodes.length; i<l; i++) {
     var method = opcodes[i][0];
@@ -9,3 +12,28 @@ export function processOpcodes(compiler, opcodes) {
     }
   }
 }
+
+let lookup = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
+var generateId;
+
+if (typeof window !== 'undefined' && window.crypto) {
+  generateId = function() {
+    let buf = new Uint8Array(12);
+    window.crypto.getRandomValues(buf);
+
+    buf = buf.map(i => i % 64);
+    return [].slice.call(buf).map(i => lookup.charAt(i)).join('');
+  };
+} else {
+  generateId = function() {
+    let buf = [];
+
+    for (let i=0; i<12; i++) {
+      buf.push(lookup.charAt(Math.floor(Math.random() * 64)));
+    }
+
+    return buf.join('');
+  };
+}
+
+export { generateId };

packages/htmlbars-compiler/tests/utils-test.js

@@ -0,0 +1,13 @@
+import { generateId } from '../htmlbars-compiler/utils';
+
+QUnit.module('generating a template ID');
+
+QUnit.test('generates a different ID every time', function() {
+  let seen = Object.create(null);
+
+  for (let i=0; i<1000; i++) {
+    seen[generateId()] = true;
+  }
+
+  equal(Object.keys(seen).length, 1000, '1000 different ids were generated');
+});