Testing file download links in an end-to-end test can be painful, especially with Selenium. The attached download_helpers.rb provides...

tl;dr With ES2021 you now can use str.replaceAll(), Promise.any(), logical assignment operators, numeric separators and WeakRef on all major...

tl;dr: Use the URLSearchParams API to make your live easier if you want to get or manipulate query parameters...

Due to the way we setup Jasmine tests in our projects, you may run into various errors when Jasmine boots...

While we are used to run our JavaScript tests on a test page within our Browser, it's also possible...

To ensure a consistent code style for JavaScript code, we use ESLint. The workflow is similar to integrating rubocop...

This are the steps I needed to do to add esbuild to an application that used the vanilla rails asset...

Building application assets with esbuild is the new way to do it, and it's great, especially in combination with...

One really simple way to check whether JavaScript Sentry integration was successful (raven-js or @sentry/browser), is to create an...

Use option:checked to find the currently selected option: select.querySelector('option:checked') Yes, :checked, not :selected. This is the same...

The Interactive Advertising Bureau (IAB) is a European marketing association which has introduced a standard how advertising can be served...

Similar to the Webpack Bundle Analyzer, Chrome's new Lighthouse feature … … shows a visualisation of your JavaScript bundles. It's...

From Exploring ES6: Module imports are hoisted (internally moved to the beginning of the current scope). Therefore, it doesn’t...

Jasmine is a great way to unit test your JavaScript components without writing an expensive end-to-end test for...

A flaky test is a test that is often green, but sometimes red. It may only fail on some PCs...

You want to use fields in your applications. However, your desktop users may encounter some weird quirks: Aside from allowing...

Event delegation is a pattern where a container element has a single event listener that handles events for all descendants...

Most browsers have built-in drag and drop support for different page elements like text and images. While this may...

Rails has the handy controller method send_file which lets us download files easily. We can decide whether the file...

It is generally discouraged to load your JavaScript by a tag in the : The reason is that a tag will pause the DOM parser until the script has loaded and executed. This will delay the browser's first contentful paint. A much better default is to load your scripts with a tag: A deferred script has many...

The attached compiler() function below applies JavaScript behavior to matching HTML elements as they enter the DOM. This works like...

Given you have a strict CSP that only allows elements from your own domain: Content-Security-Policy: script-src 'self' This will block JavaScript handlers inlined as attribute into your HTML elements. Clicking on the following link will only log an error with a strict CSP: click me click me Solution 1: Move the handler into your JavaScript The recommended solution is to move the handler from the HTML to the allowed JavaScript file that we loaded via . In the example above we could invent a new [data-alert] attribute with the alert message: click me Then our JavaScript intercepts clicks on elements with that attribute: document.addEventListener('click', function(event) { let link = event.target.closest('[data-alert]') if (link) { let message = link.dataset.alert alert(message) event.preventDefault() } }) Solution 2: Allow that one handler in your CSP Some browsers allow the CSP directive script-src-attr. This lets you allow the hashes of actual JavaScript code. The SHA256 hash of alert('hello') is vIsp2avtxDy0157AryO+jEJVpLdmka7PI7o7C4q5ABE= (in Base64). We can allow this one event handlers like this: Content-Security-Policy: script-src 'self'; script-src-attr 'unsafe-hashes' 'sha256-vIsp2avtxDy0157AryO+jEJVpLdmka7PI7o7C4q5ABE=' Note the sha256- prefix. This event handler now works when clicked: click me But any other script will still be blocked: click me Dealing with legacy browsers Currently (November 2023) about 75% of browsers support script-src-attr. Here is a forward-looking compromise that many users use with new CSP features: Have a liberal CSP with old directives supported by all browsers Make your CSP stricter with new, more specific directives for browsers that support it The CSP spec supports that approach in that using newer, more specific directives disable older, more general features. In our case this means: For old browsers, allow all inline scripts For new browsers, disallow inline scripts but allow inline handlers with given hashes Here is a CSP directive that works like this: Content-Security-Policy: script-src 'self' 'unsafe-inline'; script-src-elem 'self'; script-src-attr 'unsafe-hashes' 'sha256-vIsp2avtxDy0157AryO+jEJVpLdmka7PI7o7C4q5ABE=' Old browsers will only use script-src. New browsers will use script-src-elem (for tags) and script-src-attr (for inline event handlers), which override the more liberal rules from script-src. Solution 3: Don't use a strict CSP You can have a secure web application without a strict CSP. A Content Security Policy should never be your first line of defense against Cross-Site-Scripting (XSS). Your primary tool should be to escape and sanitize user input. Many template engines make it easy to do the right thing by escaping dynamic content by default. A CSP is a second security net. It's there when you slip up and somehow, somewhere don't sanitize user input. Depending on your project, you may decide to prioritize developer convenience over a strict CSP.

Often people need links which are not linked directly, but should trigger execution of JavaScript. ❌ Bad workarounds

You can scale background images in CSS to the container size using background-size (Demo). Commonly, we use contain or...