Detect CSS Reflows (detect-css-reflows)

Let the developers know if changes to a specific CSS property inside @keyframes will trigger changes on the Layout, Composite or Paint rendering pipeline.

Why is this important?

Understanding what rendering pipeline operations will be triggered by changes on specific CSS properties can prevent users from introducing unintentional performance hits. Paint and Layout operations should be minimized or avoided when combined with animations.

What does the hint check?

It scans the css properties inside @keyframes property against a defined set of properties and associated rendering triggers.

Examples that trigger the hint

left property triggers a Layout operation its use should be minimized inside @keyframes to avoid jankiness or slow animations.

@keyframes performance-with-layout-trigger {
    0% {
        left: 0;

    }
    100% {
        left: 400px;
    }
}

Examples that pass the hint

A better approach is to use translate which will trigger only once, at the end of the animation.

@keyframes performance-without-layout-trigger {
    0% {
        transform: translateX(0);

    }
    100% {
        transform: translateX(400px);
    }
}

Can the hint be configured?

You can decide the granularity and severity of your reports up to the following categories:

• detect-css-reflows/composite
• detect-css-reflows/layout
• detect-css-reflows/paint

How to use this hint?

To use it you will have to install it via npm:

npm install hint --save-dev

Note: You can make npm install it as a devDependency using the --save-dev parameter, or to install it globally, you can use the -g parameter. For other options see npm‘s documentation.

And then activate it via the .hintrc configuration file:

{
    "connector": {...},
    "formatters": [...],
    "parsers": [...],
    "hints": {
        "detect-css-reflows/composite": "off",
        "detect-css-reflows/layout": "hint",
        "detect-css-reflows/paint": "off"
    },
    ...
}

Further Reading