Add waitFor

wait-for.js

@@ -0,0 +1,28 @@
+/**
+ * Wait for some test to be true, returns a promise that resolves when condition is met.
+ * Useful to wait for element render, for example. Uses requestAnimationFrame.
+ *
+ * @param  {Function} testFn    Test function to call. Should return true to resolve and false to continue testing.
+ * @param  {Number}   maxTries  Maximum number of rounds to test. If exceeded, the promise rejects. Defaults to 5000.
+ * @return {Promise}  Promise that resolves when test passes or rejects when maxTries is reached
+ */
+export const waitFor = (testFn, maxTries = 5000) => {
+  return new Promise((resolve, reject) => {
+    let tries = 0;
+    const boundTestFn = testFn.bind(this);
+
+    function waiter() {
+      if (tries === maxTries) {
+        return reject(new Error('waitFor: maximum tries exceeded'));
+      }
+      if (!boundTestFn()) {
+        window.requestAnimationFrame(waiter);
+        tries++;
+        return;
+      }
+      resolve(true);
+    }
+
+    waiter();
+  });
+}