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utils for webpack loaders




Recommended way to retrieve the options of a loader invocation:

// inside your loader 
const options = loaderUtils.getOptions(this);
  1. If this.query is a string:
    • Tries to parse the query string and returns a new object
    • Throws if it's not a valid query string
  2. If this.query is object-like, it just returns this.query
  3. In any other case, it just returns null

Please note: The returned options object is read-only. It may be re-used across multiple invocations. If you pass it on to another library, make sure to make a deep copy of it:

const options = Object.assign(
    loaderUtils.getOptions(this), // it is safe to pass null to Object.assign() 
// don't forget nested objects or arrays 
options.obj = Object.assign({}, options.obj); 
options.arr = options.arr.slice();

clone-deep is a good library to make a deep copy of the options.

Options as query strings

If the loader options have been passed as loader query string (loader?some&params), the string is parsed like this:

                             -> null
?                            -> {}
?flag                        -> { flag: true }
?+flag                       -> { flag: true }
?-flag                       -> { flag: false }
?xyz=test                    -> { xyz: "test" }
?xyz=1                       -> { xyz: "1" } // numbers are NOT parsed
?xyz[]=a                     -> { xyz: ["a"] }
?flag1&flag2                 -> { flag1: true, flag2: true }
?+flag1,-flag2               -> { flag1: true, flag2: false }
?xyz[]=a,xyz[]=b             -> { xyz: ["a", "b"] }
?a%2C%26b=c%2C%26d           -> { "a,&b": "c,&d" }
?{data:{a:1},isJSON5:true}   -> { data: { a: 1 }, isJSON5: true }


Turns a request into a string that can be used inside require() or import while avoiding absolute paths. Use it instead of JSON.stringify(...) if you're generating code inside a loader.

Why is this necessary? Since webpack calculates the hash before module paths are translated into module ids, we must avoid absolute paths to ensure consistent hashes across different compilations.

This function:

  • resolves absolute requests into relative requests if the request and the module are on the same hard drive
  • replaces \ with / if the request and the module are on the same hard drive
  • won't change the path at all if the request and the module are on different hard drives
  • applies JSON.stringify to the result
loaderUtils.stringifyRequest(this, "./test.js");
// "\"./test.js\"" 
loaderUtils.stringifyRequest(this, ".\\test.js");
// "\"./test.js\"" 
loaderUtils.stringifyRequest(this, "test");
// "\"test\"" 
loaderUtils.stringifyRequest(this, "test/lib/index.js");
// "\"test/lib/index.js\"" 
loaderUtils.stringifyRequest(this, "otherLoader?andConfig!test?someConfig");
// "\"otherLoader?andConfig!test?someConfig\"" 
loaderUtils.stringifyRequest(this, require.resolve("test"));
// "\"../node_modules/some-loader/lib/test.js\"" 
loaderUtils.stringifyRequest(this, "C:\\module\\test.js");
// "\"../../test.js\"" (on Windows, in case the module and the request are on the same drive) 
loaderUtils.stringifyRequest(this, "C:\\module\\test.js");
// "\"C:\\module\\test.js\"" (on Windows, in case the module and the request are on different drives) 
loaderUtils.stringifyRequest(this, "\\\\network-drive\\test.js");
// "\"\\\\network-drive\\\\test.js\"" (on Windows, in case the module and the request are on different drives) 


Converts some resource URL to a webpack module request.

var url = "path/to/module.js";
var request = loaderUtils.urlToRequest(url); // "./path/to/module.js" 

Module URLs

Any URL containing a ~ will be interpreted as a module request. Anything after the ~ will be considered the request path.

var url = "~path/to/module.js";
var request = loaderUtils.urlToRequest(url); // "path/to/module.js" 

Root-relative URLs

URLs that are root-relative (start with /) can be resolved relative to some arbitrary path by using the root parameter:

var url = "/path/to/module.js";
var root = "./root";
var request = loaderUtils.urlToRequest(url, root); // "./root/path/to/module.js" 

To convert a root-relative URL into a module URL, specify a root value that starts with ~:

var url = "/path/to/module.js";
var root = "~";
var request = loaderUtils.urlToRequest(url, root); // "path/to/module.js" 


Interpolates a filename template using multiple placeholders and/or a regular expression. The template and regular expression are set as query params called name and regExp on the current loader's context.

var interpolatedName = loaderUtils.interpolateName(loaderContext, name, options);

The following tokens are replaced in the name parameter:

  • [ext] the extension of the resource
  • [name] the basename of the resource
  • [path] the path of the resource relative to the context query parameter or option.
  • [folder] the folder of the resource is in.
  • [emoji] a random emoji representation of options.content
  • [emoji:<length>] same as above, but with a customizable number of emojis
  • [hash] the hash of options.content (Buffer) (by default it's the hex digest of the md5 hash)
  • [<hashType>:hash:<digestType>:<length>] optionally one can configure
    • other hashTypes, i. e. sha1, md5, sha256, sha512
    • other digestTypes, i. e. hex, base26, base32, base36, base49, base52, base58, base62, base64
    • and length the length in chars
  • [N] the N-th match obtained from matching the current file name against options.regExp


// loaderContext.resourcePath = "/app/js/javascript.js" 
loaderUtils.interpolateName(loaderContext, "js/[hash].script.[ext]", { content: ... });
// => js/9473fdd0d880a43c21b7778d34872157.script.js 
// loaderContext.resourcePath = "/app/page.html" 
loaderUtils.interpolateName(loaderContext, "html-[hash:6].html", { content: ... });
// => html-9473fd.html 
// loaderContext.resourcePath = "/app/flash.txt" 
loaderUtils.interpolateName(loaderContext, "[hash]", { content: ... });
// => c31e9820c001c9c4a86bce33ce43b679 
// loaderContext.resourcePath = "/app/img/image.gif" 
loaderUtils.interpolateName(loaderContext, "[emoji]", { content: ... });
// => 👍 
// loaderContext.resourcePath = "/app/img/image.gif" 
loaderUtils.interpolateName(loaderContext, "[emoji:4]", { content: ... });
// => 🙍🏢📤🐝 
// loaderContext.resourcePath = "/app/img/image.png" 
loaderUtils.interpolateName(loaderContext, "[sha512:hash:base64:7].[ext]", { content: ... });
// => 2BKDTjl.png 
// use sha512 hash instead of md5 and with only 7 chars of base64 
// loaderContext.resourcePath = "/app/img/myself.png" 
// = 
loaderUtils.interpolateName(loaderContext, "picture.png");
// => picture.png 
// loaderContext.resourcePath = "/app/dir/file.png" 
loaderUtils.interpolateName(loaderContext, "[path][name].[ext]?[hash]", { content: ... });
// => /app/dir/file.png?9473fdd0d880a43c21b7778d34872157 
// loaderContext.resourcePath = "/app/js/page-home.js" 
loaderUtils.interpolateName(loaderContext, "script-[1].[ext]", { regExp: "page-(.*)\\.js", content: ... });
// => script-home.js 


var digestString = loaderUtils.getHashDigest(buffer, hashType, digestType, maxLength);
  • buffer the content that should be hashed
  • hashType one of sha1, md5, sha256, sha512 or any other node.js supported hash type
  • digestType one of hex, base26, base32, base36, base49, base52, base58, base62, base64
  • maxLength the maximum length in chars