Inside the source map, this is referred to as sourcesContent. It’s possible to inline your entire original source code into the source map itself. Inline your original source code into your source map via sourcesContent There are a handful of solutions for making your original source files available: Without your original source files, you’re still stuck stepping through minified code in your debugger. ![]() This likely means that your source map doesn’t contain or link to your original source files. But despite this improvement, there’s a big piece missing - you still can’t browse your original source files using your browser’s debug tools. Parts of the transformation are clearly working for example, error stack traces now mention your original filenames and contain sensible line and column locations. Let’s assume that you’ve properly generated your source map, and your sourceMappingURL (or SourceMap header) is present and correct. Many JavaScript developers may not have the capability of setting arbitrary headers on their static assets in production, so for most, it’s easier to just generate and use sourceMappingURL. Note that to serve this header, you need to configure your web server or CDN to do so. Browser agents interpret the SourceMap HTTP header and sourceMappingURL identically. Just like sourceMappingURL, if this value is a relative path, it is relative to the path location of the bundled JavaScript file. Instead of this magic sourceMappingURL comment, you can alternatively indicate the location of the source map by returning a SourceMap HTTP header value when requesting your minified file. Double-check your file in production to make sure your comment is there!Īlternatively: Ensure your server returns a valid SourceMap HTTP header Or your CDN might be doing something clever like stripping comments unknowingly Cloudflare’s Autominify feature has stripped these comments in the past. For example, another tool at the end of front-end build toolchain might be stripping comments - which would have the effect of removing //# sourceMappingURL. Note that even if you generate sourceMappingURL properly, it’s possible that it isn’t appearing once you serve your final version in production. Locate the sourceMappingURL comment at the very end of the file on its own line: To verify your source map directive is present and working, you need to: To do that, browser agents expect your bundled JavaScript files to contain either a sourceMappingURL comment or return a SourceMap HTTP header that points to the location of the source map. ![]() But generating a source map isn’t worth diddly if the browser can’t find it. We’re going to presume that you’ve already produced a source map using a tool like UglifyJS or Webpack. Missing or incorrect source map directive If you’re looking to get started with source maps for the first time, check out our earlier post, Debugging Minified JavaScript with Source Maps, before continuing. ![]() If you’ve run into some trouble, the tips below will hopefully help you get everything in working order. However, they can be tricky to get working properly. In a sense, source maps are the decoder ring to your secret (minified) code. Namely, because they are used to display your original JavaScript while debugging, which is a lot easier to look at than minified production code.
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