Warning: -file- is being assigned a //# sourceMappingURL, but already has one - JavaScript 编辑

The JavaScript warning "-file- is being assigned a //# sourceMappingURL, but already has one." occurs when a source map has been specified more than once for a given JavaScript source.

Message

Warning: -file- is being assigned a //# sourceMappingURL, but already has one.

Error type

A warning. JavaScript execution won't be halted.

What went wrong?

A source map has been specified more than once for a given JavaScript source.

JavaScript sources are often combined and minified to make delivering them from the server more efficient. With source maps, the debugger can map the code being executed to the original source files. There are two ways to assign a source map, either by using a comment or by setting a header to the JavaScript file.

Examples

Setting source maps

Setting a source map by using a comment in the file:

//# sourceMappingURL=http://example.com/path/to/your/sourcemap.map

Or, alternatively, you can set a header to your JavaScript file:

X-SourceMap: /path/to/file.js.map

See also

• How to use a source map – Firefox Tools documentation
• Introduction to source maps – HTML5 rocks