Analyze and debug JavaScript (or Sass or LESS) code bloat through source maps.

The source map explorer determines which file each byte in your minified code came from. It shows you a treemap visualization to help you debug where all the code is coming from. Check out this Chrome Developer video (3:25) for a demo of the tool in action.

Install:

npm install -g source-map-explorer

Use (you can specify filenames or use glob pattern):

source-map-explorer bundle.min.js
source-map-explorer bundle.min.js bundle.min.js.map
source-map-explorer bundle.min.js*
source-map-explorer *.js

This will open up a visualization of how the space is used in your minified bundle:

Here's a demo with a more complex bundle.

Here's another demo where you can see a bug: there are two copies of React in the bundle (perhaps because of out-of-date dependencies).

Requirements

Node 10 or later

Options

Default behavior - write HTML to a temp file and open it in your browser

source-map-explorer foo.min.js

Write output in specific formats to stdout

source-map-explorer foo.min.js --html
source-map-explorer foo.min.js --json
source-map-explorer foo.min.js --tsv

Write output in specific formats to a file

source-map-explorer foo.min.js --html result.html
source-map-explorer foo.min.js --json result.json
source-map-explorer foo.min.js --tsv result.tsv

--json: output JSON instead of displaying a visualization:

source-map-explorer foo.min.js --json
{
  "results": [
    {
      "bundleName": "tests/data/foo.min.js",
      "totalBytes": 718,
      "mappedBytes": 681,
      "unmappedBytes": 1,
      "eolBytes": 1,
      "sourceMapCommentBytes": 35,
      "files": {
        "node_modules/browser-pack/_prelude.js": {
          "size": 480
        },
        "src/bar.js": {
          "size": 104
        },
        "src/foo.js": {
          "size": 97
        },
        "[sourceMappingURL]": {
          "size": 35
        },
        "[unmapped]": {
          "size": 1
        },
        "[EOLs]": {
          "size": 1
        }
      }
    }
  ]
}

--tsv: output tab-delimited values instead of displaying a visualization:

source-map-explorer foo.min.js --tsv
Source                                  Size
node_modules/browser-pack/_prelude.js   480
src/bar.js                              104
src/foo.js                              97
[sourceMappingURL]                      35
[unmapped]                              1
[EOLs]                                  1

If you just want a list of files, you can do source-map-explorer foo.min.js --tsv | sed 1d | cut -f1.

--html: output HTML to stdout. If you want to save the output (e.g. to share), specify filename after --html:
```
source-map-explorer foo.min.js --html tree.html
```
-m, --only-mapped: exclude "unmapped" bytes from the output. This will result in total counts less than the file size.
--exclude-source-map: exclude source map comment size from output. This will result in total counts less than the file size.
--replace, --with: The paths in source maps sometimes have artifacts that are difficult to get rid of. These flags let you do simple find & replaces on the paths. For example:
```
source-map-explorer foo.min.js --replace 'dist/' --with ''
```
You can specify these flags multiple times. Be aware that the find/replace is done after eliminating shared prefixes between paths.

These are regular expressions.
--no-root: By default, source-map-explorer finds common prefixes between all source files and eliminates them, since they add complexity to the visualization with no real benefit. But if you want to disable this behavior, set the --no-root flag.
--no-border-checks: Disable invalid mapping column/line checks. By default, when a source map references column/line with bigger index than available in the source source-map-explorers throws an error indicating that specified source map might be wrong for the source.
--coverage: If the path to a valid a chrome code coverage JSON export is supplied, the tree map will be colorized according to which percentage of the modules code was executed
--gzip: Calculate gzip size. It also sets onlyMapped flag
--sort: Sort filenames

Examples

Get help

source-map-explorer -h

Analyze and debug space usage through source maps.
Usage:
source-map-explorer script.js [script.js.map] [--json [result.json] | --html [result.html] | --tsv [result.csv]] [-m | --only-mapped] [--exclude-source-map] [--no-border-checks] [--gzip] [--sort] [--replace=BEFORE_1 BEFORE_2 --with=AFTER_1 AFTER_2] [--no-root] [--coverage coverage.json] [--version] [--help | -h]
Output:
  --json  If filename specified save output as JSON to specified file otherwise output to stdout.  [string]
  --tsv   If filename specified save output as TSV to specified file otherwise output to stdout.  [string]
  --html  If filename specified save output as HTML to specified file otherwise output to stdout rather than opening a browser.  [string]
Replace:
  --replace  Apply a simple find/replace on source file names. This can be used to fix some oddities with paths that appear in the source map generation process. Accepts regular expressions.
  [array]
  --with     See --replace.  [array]
Options:
  --version             Show version number  [boolean]
  --only-mapped, -m     Exclude "unmapped" bytes from the output. This will result in total counts less than the file size  [boolean]
  --exclude-source-map  Exclude source map comment size from output  [boolean]
  --no-root             To simplify the visualization, source-map-explorer will remove any prefix shared by all sources. If you wish to disable this behavior, set --no-root.  [boolean]
  --no-border-checks    Disable invalid mapping column/line checks.  [boolean]
  --coverage            If the path to a valid a chrome code coverage JSON export is supplied, the tree map will be colorized according to which percentage of the modules code was executed
[string]
  --gzip                Calculate gzip size. It also sets onlyMapped flag  [boolean]
  --sort                Sort filenames  [boolean]
  -h, --help            Show help  [boolean]
Examples:
  source-map-explorer script.js script.js.map       Explore bundle
  source-map-explorer script.js                     Explore bundle with inline source map
  source-map-explorer dist/js/*.*                   Explore all bundles inside dist/js folder
  source-map-explorer script.js --tsv               Explore and output result as TSV to stdout
  source-map-explorer script.js --json result.json  Explore and save result as JSON to the file

Explore bundle and view result as an interactive map

source-map-explorer script.js script.js.map

Will open an HTML file containing explore result as a tree data map

Explore and output result as JSON

source-map-explorer script.js script.js.map --json

{
  "results": [
    {
      "bundleName": "script.js",
      "totalBytes": 718,
      "unmappedBytes": 1,
      "eolBytes": 1,
      "sourceMapCommentBytes": 35,
      "files": {
        "node_modules/browser-pack/_prelude.js": {
          "size": 480
        }
        "src/bar.js": {
          "size": 104
        }
        "src/foo.js": {
          "size": 97
        },
        "[sourceMappingURL]": {
          "size": 35
        }
        "[unmapped]": {
          "size": 1
        }
      }
    }
  ]
}

Explore and output result as TSV

source-map-explorer script1.js script2.js --tsv

Source  Size
node_modules/browser-pack/_prelude.js   480
src/bar.js      104
src/foo.js      97
[sourceMappingURL]      35
[unmapped]      1
[sourceMappingURL]      2308
node_modules/browser-pack/_prelude.js   480
src/bar.js      104
src/foo.js      97
[unmapped]      1

Explore and output result as HTML

source-map-explorer script.js --html