In Selenium’s JavaScript binding, use async functions and await to sequence WebDriver commands, then use driver.wait() to wait for a meaningful page condition. Use executeAsyncScript() only when you need asynchronous JavaScript to run in the page itself; that script must call Selenium’s injected completion callback.
Use async/await for Selenium commands in JavaScript tests
Selenium’s JavaScript WebDriver methods return promises. Mark the test or helper function async, then await each command whose result or completion the next step depends on. This keeps browser actions in order and lets rejected commands flow through normal JavaScript error handling.
const { Builder, By, until } = require('selenium-webdriver');
async function example() {
const driver = await new Builder().forBrowser('chrome').build();
try {
await driver.get('https://example.test');
const button = await driver.wait(
until.elementLocated(By.id('continue')),
10_000
);
await button.click();
await driver.wait(until.titleIs('Next step'), 10_000);
} finally {
await driver.quit();
}
}
example().catch(error => {
console.error(error);
process.exitCode = 1;
});This is a JavaScript-binding example. The Selenium API methods and examples are documented in the Selenium WebDriver JavaScript API. The finally block attempts to close the browser whether the test succeeds or throws; handling the rejected top-level promise makes failures visible to the test process.
Wait for application state, not an arbitrary delay
Awaiting a command means waiting for that WebDriver operation’s promise to settle. It does not necessarily mean that the application has finished rendering or that the next UI state is ready. For that, use an explicit condition wait. Selenium’s JavaScript driver.wait(condition, timeout) repeatedly evaluates a condition, including promise-like conditions, until it becomes truthy or the timeout expires.
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- Use
until.elementLocated()when the element must appear in the DOM. - Use a visibility condition when the element must be visible before interacting with it.
- Wait for a meaningful result after an action, such as a changed title or a confirmation element, rather than assuming that the click itself means the page is ready.
A fixed sleep only delays the test for a predetermined duration. It neither proves that the application is ready nor adapts when the page responds faster or slower. Selenium’s wait methods and conditions are described in the JavaScript API documentation.
Know which context is running your JavaScript
There are two different forms of “async” in Selenium JavaScript. await driver.get(...) runs in the Node.js test process and waits for a WebDriver command’s promise. driver.executeAsyncScript(...) runs a function in the selected browser frame and waits for that page-side function to call Selenium’s injected callback. They solve different problems.
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| Need | Use | How completion is signaled |
|---|---|---|
| Sequence WebDriver actions in a JavaScript test | async function and await driver calls |
The WebDriver promise resolves or rejects |
| Wait until a UI condition becomes true | driver.wait(condition, timeout) |
The condition becomes truthy, or the wait times out |
| Run asynchronous work in the selected page frame and return a value | driver.executeAsyncScript(...) |
The page function calls Selenium’s injected callback |
Use executeAsyncScript for page-side asynchronous work
Choose executeAsyncScript() when the test needs to start or observe asynchronous work inside the browser context and return its result through WebDriver. Selenium appends a completion callback as the final argument to the injected function. The function must invoke it; otherwise the command remains pending until the script timeout.
const value = await driver.executeAsyncScript(function () {
const done = arguments[arguments.length - 1];
fetch('/api/status')
.then(response => response.json())
.then(data => done(data.status))
.catch(error => done({ error: String(error) }));
});The function is serialized and executed in the page, so it cannot rely on lexical variables from the Node.js process. Values needed by the page function must be made available to it through arguments or page state. Do not assume returning a Promise from the injected function makes Selenium wait for that Promise: the documented completion mechanism is calling the injected callback. See the executeAsyncScript API reference.
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Set a bounded script timeout
The script timeout limits how long WebDriver waits for an asynchronous page script to call its callback. Selenium’s JavaScript WebDriver implementation documentation specifies a default of 30,000 milliseconds. Treat that as the documented default for that implementation, not a guarantee across every binding or installed version; confirm the behavior for the version you use. Configure the timeout to cover the expected operation while remaining bounded. See the JavaScript WebDriver API.
Timeout configuration is binding-specific. Python uses driver.set_script_timeout(seconds) with execute_async_script(); Java exposes JavascriptExecutor.executeAsyncScript and uses WebDriver’s timeout API. Those method names and syntax are not interchangeable with JavaScript’s API. See the Python API reference and Java JavascriptExecutor reference.
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Troubleshoot common async and await problems
- The next test step runs before the prior WebDriver action completes: add
awaitto the relevant driver call inside anasyncfunction, and await the helper if it returns a promise. - The test proceeds but the UI is not ready: awaiting a navigation or click waits for that command, not every application update. Add a condition-based
driver.wait()for the expected state. executeAsyncScript()times out: ensure every success and error path calls the injected callback. If the page operation can legitimately take longer, adjust the script timeout within a reasonable bound.- The injected function cannot find a Node.js variable: the function executes in the page context and does not close over Node.js lexical scope. Pass the required data into the page-side function or read it from page state.
- A sleep fixes one run but not another: replace the fixed duration with a wait for the specific element or state the next action requires.
- Timeout code copied from another language fails: check the API for the binding actually used. Python’s
set_script_timeout, Java’s timeout API, and JavaScript WebDriver methods have different interfaces.
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