ParserBlockingJavaScript
Identifies HTML script tags that don't have defer
or async
attributes.
When neither of those attributes are used, a script tag blocks the construction and rendering of the DOM until the script is loaded, parsed and executed. It also creates congestion on the network, messes with the resource priorities and significantly delays the rendering of the page.
Considering that JavaScript on Shopify themes should always be used to progressively enhance the experience of the site, themes should never make use of parser-blocking script tags.
As a general rule, use defer
if the order of execution matters, and use async
if it doesn't.
Learn more about improving your theme's performance.
Anchor to ExamplesExamples
The following examples contain code snippets that either fail or pass this check.
Anchor to ✗ Fail✗ Fail
This example loads jQuery synchronously because inline scripts depend on it:
Anchor to ✓ Pass✓ Pass
This example contains an alternative to synchronous jQuery. Because the script tag has a defer
attribute, jQuery is guaranteed to be loaded when DOMContentLoaded fires. This technique could be used as a first step to refactor an theme that depends on jQuery.
Theme Check only lints script tags that include the src
attribute.
This example avoids jQuery.
Anchor to OptionsOptions
The following example contains the default configuration for this check:
Parameter | Description |
---|---|
enabled | Whether this check is enabled. |
severity | The severity of the check. |
Anchor to Disabling this checkDisabling this check
If you can't avoid violating the rule, you should disable the check using the comment syntax. This ensures that you intentionally disable the check for each instance.
Disabling this check isn't recommended.