The <script> Element

Technical Summary

Definition / Variants

Variant	Selection point	Processing summary
Classic script	No type, or a JavaScript MIME type	Evaluated as ordinary JavaScript. Without timing attributes, it blocks parsing while it is fetched and evaluated
Module script	type="module"	Fetches module dependencies and evaluates after parsing by default
Data block	A non-JavaScript type	Not evaluated as a script; an application can read its contents as data

The type attribute is therefore a processing condition, not merely a label for presentation.

Processing order

Condition	Fetching	Evaluation
classic / external / no timing attribute	Fetched while parsing	Immediately after fetching; parsing is paused
classic / external / async	In parallel with parsing	When ready; order is not guaranteed
classic / external / defer	In parallel with parsing	After parsing, in document order
module	Fetched with its module dependencies	After parsing by default; async can select earlier evaluation

classic + no async/defer  → fetch → evaluate → continue parsing
classic + async          → fetch in parallel → evaluate when ready
classic + defer          → fetch in parallel → evaluate after parsing
module                   → fetch dependencies → evaluate after parsing

Attributes and boundaries

• srcSpecifies the external script source URL. An element using an external source should not also contain executable source text.
• typeSelects a classic script, module script, data block, or another defined processing mode.
• async / deferSelects fetching and evaluation timing for relevant external scripts. defer has no effect on module scripts.
• policyCSP is a separate policy boundary and can prevent an otherwise valid script from executing.

Fetch and failure boundary

Processing does not end when the element's kind is selected. Fetching the source, fetching module dependencies, CORS, and CSP can all affect whether evaluation proceeds. In particular, cross-origin module scripts require the CORS protocol.

source markup
  ↓ determine script kind
  ↓ apply policy gates
  ↓ fetch source / module dependencies
  ↓ evaluate or expose data block

Fact / Evidence

Key facts are mapped to their conditions, review status, and evidence locations. Unresolved scope remains visible in the Coverage section below.

Evidence

1. HTML Standard: The script element — element kinds, attributes, and processing model
2. HTML Standard: Scripting, Edition for Web Developers — async, defer, and module evaluation timing
3. Fetch Standard — external resource fetching and CORS boundaries

Implementation Evidence

Implementation observations are recorded separately from normative claims. Unrun items are not treated as reviewed.

Shared fixture / environment: One HTML document with a classic script, an application/json data block, an inline module, and a dynamically inserted classic script. Chrome 152.0.0.0 / Windows NT 10.0 / checked 2026-09-13.

Use the WPT repository for test mapping and HTML-AAM for accessibility criteria.

Coverage / Open Issues

• ReviewedClassic, module, and data-block distinctions; the basic timing model for async and defer
• OpenComplete processing branches, parser insertion, and dynamic insertion paths
• OpenCross-Spec details for CSP, Fetch, CORS, Referrer Policy, and Integrity
• OpenThis implementation and AX observation covers one Chrome environment only. External async/defer scripts, multi-browser comparison, WPT, historical changes, and operational differences remain unregistered.

This is initial coverage. It does not claim that every fact about the script element has been verified or that every implementation produces the same result.

Related surface

For minimal examples and guidance on choosing defer, async, or modules, see the script element page in Yugien.