Darren Hebner 09/20/2019

Want to Improve UI Performance? Start by Understanding Your User

My team at Shopify recently did a deep dive into the performance of the Marketing section in the Shopify admin. Our focus was to improve the UI performance. This included a mix of improvements that affected load time, perceived load time, as well as any interactions that happen after the merchant has landed in our section.

It’s important to take the time to ask yourself what the user (in our case, merchant) is likely trying to accomplish when they visit a page. Once you understand this, you can try to unblock them as quickly as possible. We as UI developers can look for opportunities to optimize for common flows and interactions the merchant is likely going to take. This helps us focus on improvements that are user centric instead of just trying to make our graphs and metrics look good.

I’ll dive into a few key areas that we found made the biggest impact on UI performance:

  • How to assess your current situation and spot areas that could be improved
  • Prioritizing the loading of components and data
  • Improving the perceived loading performance by taking a look at how the design of loading states can influence the way users experience load time.

Our team has always kept performance top of mind. We follow industry best practices like route-based bundle splitting and are careful not to include any large external dependencies. Nevertheless, it was still clear that we had a lot of room for improvement.

The front end of our application is built using React, GraphQL, and Apollo. The advice in this article aims to be framework agnostic, but there are some references to React specific tooling.

Assess Your Current Situation

Develop Merchant Empathy by Testing on Real-World Devices

In order to understand what needed to be improved, we had to first put ourselves in the shoes of the merchant. We wanted to understand exactly what the merchant is experiencing when they use the Marketing section. We should be able to offer merchants a quality experience no matter what device they access the Shopify admin from.

We think testing using real, low-end devices is important. Testing on a low-end device allows us to ensure that our application performs well enough for users who may not have the latest iPhone or Macbook Pro.

Moto G3
Moto G3 Device

We grabbed a Moto G3 and connected the device to Chrome developer tools via the remote devices feature. If you don’t have access to a real device to test with, you can make use of webpagetest.org to run your application on a real device remotely.

Capture an Initial Profile

Our initial performance profile captured using Chrome Developer tools.
Our initial performance profile captured using Chrome Developer tools

After capturing our initial profile using the performance profiler included in the Chrome developer tools, we needed to break it down. This profile gives us a detailed timeline of every network request, JavaScript execution, and event that happens during our recording plus much, much more. We wanted to understand exactly what is happening when a merchant interacts with our section.

We ran the audit with React in development mode so we could take advantage of the user timings they provide. Running the application with React in production mode would have performed better, but having the user timings made it much easier to identify which components we need to investigate.

React profiler by React dev tools
React Profiler from React Dev Tools

We also took the time to capture a profile using the profiler provided by React dev tools. This tool allowed us to see React specific details like how long it took to render a component or how many times that component has been updated. The React profiler was particularly useful when we sorted our components from slowest to fastest.

Get Our Priorities in Order

After reviewing both of these profiles, we were able to take a step back and gain some perspective. It became clear that our priorities were out of order.

We found that the components and data that are most crucial to merchants were being delayed by components that could have been loaded at a later time. There was a big opportunity here to rearrange the order of operations in our favor with the ultimate goal of making the page useful as soon as possible.

We know that the majority of visits to the Marketing section are incremental. This means that the merchant navigated to the Marketing section from another page in the admin. Because the admin is a single page app, these incremental navigations are all handled client side (in our case using React Router). This means that traditional performance metrics like time to first byte or first meaningful paint may not be applicable. We instead make use of the Navigation Timing API to track navigations within the admin.

When a merchant visits the Marketing section, the following events happen:

  • JavaScript required to render the page is fetched
  • A GraphQL query is made for the data required for the page
  • The JavaScript is executed and our view is rendered with our data

Any optimizations we do will be to improve one of those events. This could mean fetching less data and JavaScript, or making the execution of the JavaScript faster.

Deprioritize Non-Essential Components and Code Execution

We wanted the browser to do the least amount of work necessary to render our page. In our case, we were asking the browser to do work that did not immediately benefit the merchant. This low-priority work was getting in the way of more important tasks. We took two approaches to reducing the amount of work that needed to be done:

  • Identifying expensive tasks that are being run repeatedly and memoize (~cache) them.
  • Identifying components that are not immediately required and deferring them.

Memoizing Repetitive and Expensive Tasks

One of the first wins here was around date formatting. The React profiler was able to identify one component that was significantly slower than the rest of the components on the page.

React Profiler Identifying <StartEndDates /> Component is Significantly Slower
React Profiler Identifying <StartEndDates /> Component is Significantly Slower

The <StartEndDates /> component stood out. This component renders a calendar that allows merchants to select a start and end date. After digging into this component, we discovered that we were repeating a lot of the same tasks over and over. We found that we were constructing a new Intl.DateTimeFormat object every time we needed to format a date. By creating a single Intl.DateTimeFormat object and referencing it every time we needed to format a date, we were able to reduce the amount of work the browser needed to do in order to render this component.

<StartEndDates /> after memoization of two other date formatting utilities
<StartEndDates /> after memoization of two other date formatting utilities

This in combination with the memoization of two other date formatting utilities resulted in a drastic improvement in this components render time. Taking it from ~64.7 ms down to ~0.5 ms.

Defer Non-Essential Components

Async loading allows us to load only the minimum amount of JavaScript required to render our view. It is important to keep the JavaScript we do load small and fast as it contributes to how quickly we can render the page on navigation.

One example of a component that we decided to defer was our <ImagePicker />. This component is a modal that is not visible until the merchant clicks a Select image button. Since this component is not needed on the initial load, it is a perfect candidate for deferred loading.

By moving the JavaScript required for this component into a separate bundle that is loaded asynchronously, we were able to reduce the size of the bundle that contained the JavaScript that is critical to rendering our initial view.

Get a Head Start

Prefetching the image picker when the merchant hovers over the activator button makes it feel like the modal instantly loads.
Prefetching the image picker when the merchant hovers over the activator button makes it feel like the modal instantly loads

Deferring the loading of components is only half the battle. Even though the component is deferred, it may still be needed later on. If we have the component and its data ready when the merchant needs it, we can provide an experience that really feels instant.

Knowing what a merchant is going to need before they explicitly request it is not an easy task. We do this by looking for hints the merchant provides along the way. This could be a hover, scrolling an element in to the viewport, or common navigation flows within the Shopify admin.

In the case of our <ImagePicker /> modal, we do not need the modal until the Select image button is clicked. If the merchant hovers over the button, it’s a pretty clear hint that they will likely click. We start prefetching the <ImagePicker /> and its data so by the time the merchant clicks we have everything we need to display the modal.

Improve the Loading Experience

In a perfect world, we would never need to show a loading state. In cases where we are unable to prefetch or the data hasn’t finished downloading, we fallback to the best possible loading state by using a spinner or skeleton content. We typically choose to use a skeleton if we have an idea what the final content would look like.

Use Skeletons

Skeleton content has emerged as a best practice for loading states. When done correctly, skeletons can make the merchant feel like they have ‘arrived’ at the next state before the page has finished loading.

Skeletons are often not as effective as they could be. We found that it’s not enough to put up a skeleton and call it a day. By including static content that does not rely on data from our API, the page will feel a lot more stable as data arrives from the server. The merchant feels like they have ‘arrived’ instead of being stuck in an in between loading state.

Animation showing how adding headings helps the merchant understand what content they can expect as the page loads.
Animation showing how adding headings helps the merchant understand what content they can expect as the page loads

Small tweaks like adding headings to the skeleton go a long way. These changes give the merchant a chance to scan the page and get a feel for what they can expect once the page finishes loading. They also have the added benefit of reducing the amount of layout shift that happens as data arrives.

Improve Stability

When navigating between pages, there are often going to be several loading stages. This may be caused by data being fetched from multiple sources, or the loading of resources such as images or fonts.

As we move through these loading stages, we want the page to feel as stable as possible. Drastic changes to the pages layout are disorienting and can even cause the user to make mistakes.

Using a skeleton to help improve stability by matching the height of the skeleton to the height of the final content as closely as possible.
Using a skeleton to help improve stability by matching the height of the skeleton to the height of the final content as closely as possible

Here’s an example how we used a skeleton to help improve stability. The key is to match the height of the skeleton to the height of the final content as closely as possible.

Make the Page Useful as Quickly as Possible

Rendering the ‘Create campaign’ button while we are still in the loading state
Rendering the Create campaign button while we are still in the loading state

In this example, you can see that we are rendering the Create campaign button while we are still in the loading state. We know this button is always going to be rendered, so there’s no sense in hiding it while we are waiting for unrelated data to arrive. By showing this button while still in the loading state, we unblock the merchant.

No Such Thing as Too Fast

The deep dive helped our team develop best practices that we are able to apply to our work going forward. It also helped us refine a performance mindset that encourages exploration. As we develop new features, we can apply what we’ve learned while always trying to improve on these techniques. Our focus on performance has spread to other disciplines like design and research. We are able to work together to build up a clearer picture of the merchants intent so we can optimize for this flow.


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