Headers: SourceMap

SourceMap header

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.

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See full compatibility

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

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: text/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 format specification> # sec-linking-http-header>

Browser compatibility

	Desktop					Mobile
	Chrome	Edge	Firefox	Opera	Safari	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet	WebView Android	WebView on iOS
`SourceMap`	18 Not supported for ECMAScript Modules (`<script type="module">`). See bug 40854862. 18	79 Not supported for ECMAScript Modules (`<script type="module">`). See bug 40854862. 79	5527	15 Not supported for ECMAScript Modules (`<script type="module">`). See bug 40854862. 15	76	18 Not supported for ECMAScript Modules (`<script type="module">`). See bug 40854862. 18	5527	14 Not supported for ECMAScript Modules (`<script type="module">`). See bug 40854862. 14	76	1.0 Not supported for ECMAScript Modules (`<script type="module">`). See bug 40854862. 1.0	4.4 Not supported for ECMAScript Modules (`<script type="module">`). See bug 40854862. 4.4	76