feat: support

src/page.ts

@@ -1,3 +1,5 @@
+import { deadline } from "https://deno.land/[email protected]/async/deadline.ts";
+
 import { Celestial, Network_Cookie } from "../bindings/celestial.ts";
 import { Browser } from "./browser.ts";
 import { ElementHandle } from "./elementHandle.ts";
@@ -35,6 +37,8 @@ export type WaitForNetworkIdleOptions = {
   idleConnections?: number;
 };
 
+export type EvalFunc<T> = string | (() => T);
+
 export class Page {
   #id: string;
   #celestial: Celestial;
@@ -193,7 +197,7 @@ export class Page {
    * const innerHTML = await page.evaluate(()=>document.body.innerHTML)
    * ```
    */
-  async evaluate<T>(func: string | (() => T)) {
+  async evaluate<T>(func: EvalFunc<T>) {
     if (typeof func === "function") {
       func = `(${func.toString()})()`;
     }
@@ -302,6 +306,25 @@ export class Page {
     return convertToUint8Array(data);
   }
 
+  /**
+   * Runs a function in the context of the page until it returns a truthy value.
+   */
+  async waitForFunction<T>(func: EvalFunc<T>) {
+    // TODO(lino-levan): Make this easier to read
+    await deadline(
+      (async () => {
+        while (true) {
+          const result = await this.evaluate(func);
+
+          if (result) {
+            return result;
+          }
+        }
+      })(),
+      this.timeout,
+    );
+  }
+
   /**
    * Waits for the page to navigate to a new URL or to reload. It is useful when you run code that will indirectly cause the page to navigate.
    */

tests/__snapshots__/wait_test.ts.snap

@@ -0,0 +1,3 @@
+export const snapshot = {};
+
+snapshot[`Wait for function 1`] = `undefined`;

tests/wait_test.ts

@@ -1,3 +1,4 @@
+import { assertSnapshot } from "https://deno.land/[email protected]/testing/snapshot.ts";
 import { launch } from "../mod.ts";
 
 Deno.test("Wait for selector", async () => {
@@ -14,3 +15,21 @@ Deno.test("Wait for selector", async () => {
   // Close browser
   await browser.close();
 });
+
+Deno.test("Wait for function", async (t) => {
+  // Launch browser
+  const browser = await launch();
+
+  // Open the webpage
+  const page = await browser.newPage("https://pyro.deno.dev");
+
+  // Wait for function (kind of a stupid case, but whatever, make it better if you see this)
+  const fetched = await page.waitForFunction(async () => {
+    const req = await fetch("https://pyro.deno.dev/guides/");
+    return await req.text();
+  });
+  assertSnapshot(t, fetched);
+
+  // Close browser
+  await browser.close();
+});