implement #wait_for_selector method for browser

lib/ferrum/browser.rb

@@ -28,7 +28,7 @@ class Browser
                 evaluate evaluate_on evaluate_async execute evaluate_func
                 add_script_tag add_style_tag bypass_csp
                 on goto position position=
-                playback_rate playback_rate=] => :page
+                playback_rate playback_rate= wait_for_selector] => :page
     delegate %i[default_user_agent] => :process
 
     attr_reader :client, :process, :contexts, :logger, :js_errors, :pending_connection_errors,

lib/ferrum/frame/dom.rb

@@ -36,6 +36,36 @@ def body
         evaluate("document.documentElement.outerHTML")
       end
 
+      def wait_for_selector(css: nil, xpath: nil, timeout: 1000, interval: 100)
+        tap do
+          evaluate_func(%(
+            function(selector, isXpath, timeout, interval) {
+              var attempts = 0;
+              var max = timeout / interval;
+              function waitForSelector(resolve, reject) {
+                if (attempts > ((max < 1) ? 1 : max)) {
+                  return reject(new Error("Not found element match the selector:" + selector));
+                }
+                var element = isXpath
+                  ? document.
+                      evaluate(selector, document, null, XPathResult.FIRST_ORDERED_NODE_TYPE, null).singleNodeValue
+                  : document.querySelector(selector);
+                if (element !== null) {
+                  return resolve(element);
+                }
+                setTimeout(function () {
+                  waitForSelector(resolve, reject);
+                }, interval);
+                attempts++;
+              }
+              return new Promise(function (resolve, reject) {
+                waitForSelector(resolve, reject);
+              });
+            }
+          ), css || xpath, css.nil? && !xpath.nil?, timeout, interval, awaitPromise: true)
+        end
+      end
+
       def xpath(selector, within: nil)
         expr = <<~JS
           function(selector, within) {

lib/ferrum/page.rb

@@ -34,7 +34,7 @@ def reset
     delegate %i[at_css at_xpath css xpath
                 current_url current_title url title body doctype content=
                 execution_id evaluate evaluate_on evaluate_async execute evaluate_func
-                add_script_tag add_style_tag] => :main_frame
+                add_script_tag add_style_tag wait_for_selector] => :main_frame
 
     include Animation
     include Screenshot

spec/browser_spec.rb

@@ -504,6 +504,64 @@ module Ferrum
       expect(browser.evaluate("window.last_hashchange")).to eq("#foo")
     end
 
+    context "wait_for_selector" do
+      before do
+        browser.go_to("/ferrum/with_js")
+      end
+
+      it "waits for provided css selector" do
+        expect(
+          browser.wait_for_selector(css: "div#wait_for_selector").at_css("div#wait_for_selector")
+        ).not_to be_nil
+      end
+
+      it "waits for provided css hidden selector" do
+        expect(
+          browser.wait_for_selector(css: "div#wait_for_hidden_selector").at_css("div#wait_for_hidden_selector")
+        ).not_to be_nil
+      end
+
+      it "waits for provided xpath selector" do
+        expect(
+          browser.wait_for_selector(xpath: "//div[@id='wait_for_selector']").at_css("div#wait_for_selector")
+        ).not_to be_nil
+      end
+
+      it "waits for provided xpath hidden selector" do
+        expect(
+          browser
+            .wait_for_selector(xpath: "//div[@id='wait_for_hidden_selector']")
+            .at_css("div#wait_for_hidden_selector")
+        ).not_to be_nil
+      end
+
+      it "raises error when timeout exceed" do
+        expect do
+          browser.wait_for_selector(css: "div#wait_for_selector", timeout: 800)
+        end.to raise_error(Ferrum::JavaScriptError, /Not found element match the selector/)
+      end
+
+      it "raises error when provided invalid css" do
+        expect do
+          browser.wait_for_selector(css: "//div[@id='wait_for_selector']")
+        end.to raise_error(Ferrum::JavaScriptError, /Failed to execute 'querySelector' on 'Document'/)
+      end
+
+      it "raises error when provided invalid xpath" do
+        expect do
+          browser.wait_for_selector(xpath: "div#wait_for_selector")
+        end.to raise_error(Ferrum::JavaScriptError, /Failed to execute 'evaluate' on 'Document'/)
+      end
+
+      it "waits less than provided timeout when node found" do
+        Timeout.timeout(1) do
+          expect(
+            browser.wait_for_selector(css: "div#wait_for_selector", timeout: 2000).at_css("div#wait_for_selector")
+          ).not_to be_nil
+        end
+      end
+    end
+
     context "current_url" do
       it "supports whitespace characters" do
         browser.go_to("/ferrum/arbitrary_path/200/foo%20bar%20baz")

spec/support/views/with_js.erb

@@ -24,6 +24,23 @@
         display: inline;
       }
     </style>
+    <script>
+      $(document).ready(function(){
+        setTimeout(function(){
+          const div = document.createElement('div');
+          div.setAttribute('id', 'wait_for_selector');
+          document.body.appendChild(div);
+        }, 900);
+      });
+      $(document).ready(function(){
+        setTimeout(function(){
+          const div = document.createElement('div');
+          div.setAttribute('id', 'wait_for_hidden_selector');
+          div.setAttribute('style', 'display:none;');
+          document.body.appendChild(div);
+        }, 900);
+      });
+    </script>
   </head>
 
   <body>