SeleniumEngineJS

Selenium-like methods useful for automating SPAs (Single Page Application) where content is changed dynamically.

Introduction

This little script written in vanilla JS tries to emulate some of the Selenium most useful features, such as the Expected Conditions. It was originally written to be included into Tampermonkey/Greasemonkey scripts to bring the power of selenium into user scripts and be able to automate even Single Page Applications (where usually content and elements are loaded dynamically and URLs don't change, making automation really hard).

The script itself uses Promises but the real deal is the use of async/await in your code to chain Promises in a cleaner way so that async code looks as if it was syncronous (but IT IS NOT, don't get confused).

As of February 2022, async/await keywords are supported everywhere EXCEPT Internet Explorer, which does not even support Promises thus making this script completely useless (but i think almost nobody is still using it 😄).

Even without async/await you could still chain the operations by using Promise.then(), but it is just another way of going down the good old callback hell 😟.

How to use

Browser

In your HTML file, by using a CDN

• JSDelivr (preferred):

<script type="text/javascript" src="https://cdn.jsdelivr.net/npm/selenium-engine-js/src/SeleniumEngine.min.js"></script>

• UnPkg:

<script type="text/javascript" src="https://unpkg.com/selenium-engine-js/src/SeleniumEngine.js"></script>

Javascript

• using import (preferred):

(async () => {
	// ...
	await import("https://cdn.jsdelivr.net/npm/selenium-engine-js/src/SeleniumEngine.min.js");
	// ...
})()

• using eval:

fetch("https://cdn.jsdelivr.net/npm/selenium-engine-js/src/SeleniumEngine.min.js")
	.then(data => data.text())
	.then(body => eval(body));

NodeJS

Install

npm install selenium-engine-js

Use in your code

• NodeJS (CJS)

const SeleniumEngine = require("selenium-engine-js");

• NodeJS (ESModules):

import SeleniumEngine from "selenium-engine-js";

Methods

Important

All the methods MUST be used inside an async function, as for the examples below (or using Promise.then(), which, again, is discouraged since it kinda destroys the whole concept behind this project).

SeleniumEngine.waitUntil(testCondition, timeout_ms, checkInterval_ms)

Used internally by SeleniumEngine.waitForElementPresent() and SeleniumEngine.waitForElementNotPresent(). Pauses the execution of the current function until the provided function testCondition is truthy (the function is executed every checkInterval_ms ms, default is 1000).

Throws an error if wait time exceeds timeout_ms (default is 30000).

(async () => {
    console.log("Operation 1");

    try {
        let test_switch = false;
        window.setTimeout(() => { test_switch = true}, 4500);


        // Example 1 - Returns after the variable `test_switch` has become true
        let resp = await SeleniumEngine.waitUntil(() => test_switch == true)
        console.log("Now we can continue with the example. We have waited for %d ms", resp.time)


        // Example 2 - Throws an error like `Timeout of 30000ms exceeded (30016 real)`
        await SeleniumEngine.waitUntil(() => false)
        console.log("This won't be executed")

    } catch (err) {
        console.log("As expected, the second example has returned an exception: %o", err)
    }


    // Example 3 - Will wait forever, because timeout is disabled and the expected condition is NEVER met
    console.warn("The next expression will wait forever, because timeout is disabled")
    await SeleniumEngine.waitUntil(() => false, 0);


    console.log("Operation 2");
})()

See it live

SeleniumEngine.waitForElementPresent(cssSelector, timeout_ms)

Pauses the execution of the current function until an element matching the provided CSS selector is found.

Throws an exception if it isn't found before timeout_ms ms

// 1. Here we create an element with ID=test and we append to the body after 5000ms
window.setTimeout(() => {
    const test_element = document.createElement("span");
    test_element.id = "test";
    
    document.body.appendChild(test_element);
}, 5000);


// 2. Here we wait until the element is present in the page
(async () => {
    console.log("Operation 1");
    
    // Pause function for 5 seconds, then continues
    await SeleniumEngine.waitForElementPresent("#test", 8000)

    console.log("Operation 2");
})()

SeleniumEngine.waitForElementNotPresent(cssSelector, timeout_ms)

Pauses the execution of the current function until an element matching the provided CSS selector is no longer found

Throws an exception if it isn't found before timeout_ms ms

// 1. Here we remove the element with ID=test after 5000ms
(() => {
    const test_element = document.createElement("span");
    test_element.id = "test";
    document.body.appendChild(test_element);

    // Then after 5 seconds we remove it
    window.setTimeout(() => {
        document.getElementById("test").remove()
    }, 5000);
})()


// 2. Here we wait until the element is not present anymore in the page
(async () => {
    console.log("Operation 1");
    
    // Pause function for 5 seconds, then continues
    await SeleniumEngine.waitForElementNotPresent("#test", 8000)

    console.log("Operation 2");
})()

SeleniumEngine.sleep(ms)

Pauses the execution of the current function for the number of milliseconds passed as parameter.

(async () => {
    console.log("Operation 1");
    
    // Pause function for 2 seconds
    await SeleniumEngine.sleep(2000);

    console.log("Operation 2");
})()

See it live