SourceMap
Baseline Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since January 2020.
The HTTP SourceMap response header provides the location of a source map for the resource.
The HTTP SourceMap header has precedence over a source annotation (sourceMappingURL=path-to-map.js.map), and if both are present, the header URL is used to resolve the source map file.
| Header type | Response header |
|---|---|
| Forbidden header name | No |
Syntax
SourceMap: <url>
X-SourceMap: <url> (deprecated)
Directives
<url>-
A relative (to the request URL) or absolute URL pointing to a source map file.
Examples
Linking to a source map using the SourceMap header
The following response contains an absolute path in the SourceMap header.
HTTP/1.1 200 OK
Content-Type: application/javascript
SourceMap: /path/to/file.js.map
<optimized-javascript>
Developer tools use the source map to reconstruct the original source from the optimized JavaScript returned in the response, allowing developers to debug the original code rather than the format that has been optimized for sending.
Specifications
| Specification |
|---|
| Source Map specification # linking-generated-code |
Browser compatibility
BCD tables only load in the browser
See also
- Source map
- Firefox Developer Tools: using a source map
- What are source maps? on web.dev (2023)