The best way to avoid JavaScript performance issues is to encourage developers to use Google Chrome’s DevTools (or similar solutions) to profile and optimize JavaScript during development. Get the Ebook Putting the Pieces Together LoadNinja makes it easy to develop browser-based tests to measure JavaScript performance and identify bottlenecks. By measuring the time between the request and the final render, you have a much clearer picture of the user experience – especially for JavaScript-heavy apps. Of course, these tests fail to account for the time it takes a browser to load JavaScript, CSS, images and other assets.īrowser-based load tests overcome these issues by spinning up actual browser instances and measuring how long it takes them to fully render a response. They send a request to a server endpoint and measure the response time and other performance metrics. Most load testing solutions are protocol-based platforms, which means that they only test server endpoints. From there, you may want to look for ways to make the line of code more efficient to reduce the impact on page load. You can go to the exact line of JavaScript code causing an issue by clicking on the relevant file at the bottom of the Summary tab. If you click on a particular call, you can see how long it took to execute.Ĭhrome DevTools Script Overview – Source: Google The flame chart shows activity on the main CPU thread over time, where the X-Axis is time and the Y-Axis is the call stack. If you’re seeing a laggy UI or excessive CPU usage, you can debug performance issues in the Main section under the Performance tab. If you’re maxing out a browser’s CPU, find ways to cut down on the amount of work necessary because you could be slowing down the user’s device. CPU Chart: The CPU chart shows the browser’s CPU usage.When the framerate drops below acceptable levels, you’ll see a red bar rather than a green bar.

FPS Chart: The Frames per Second (FPS) chart shows the performance of animations and should generally be 60 FPS.

There are a couple of key metrics to watch: You can also throttle network speed to simulate mobile networks. For instance, you may want to set CPU to “2x slowdown” to mimic a mobile device if you’re on a high-powered laptop.

Note: You can throttle Network or CPU resources in the top section of the Performance Tab. Chrome DevTools Performance Reports – Source: Google

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