Source Map Support

This module provides source map support for stack traces in node via the V8 stack trace API. It uses the source-map module to replace the paths and line numbers of source-mapped files with their original paths and line numbers. The output mimics node's stack trace format with the goal of making every compile-to-JS language more of a first-class citizen. Source maps are completely general (not specific to any one language) so you can use source maps with multiple compile-to-JS languages in the same node process.

Installation

npm install source-map-support

This module takes effect globally and should be initialized by inserting require('source-map-support').install() at the top of your code.

Usage

To use a valid source map (generated using something like source-map-index-generator), the compiled code should contain the following two extra lines:

//@sourceMappingURL=path/to/sourceMapFile.json
require('source-map-support').install();

Demos

Basic Demo

original.js:

throw new Error("test");

compiled.js:

//#sourceMappingURL=original.sourcemap.json
require('source-map-support').install();

throw new Error("test");

original.sourcemap.json:

{"version":3,"file":"compiled.js","sources":["original.js"],"names":[],"mappings":";;;AAAA,CAAC,CAAC,CAAC,CAAC,CAAC,CAAC,CAAC,CAAC"}

After running compiled.js you should get the following outout:

/path/to/original.js:1
throw new Error("test");
      ^
Error: test
    at Object.<anonymous> (/path/to/original.js:1:7)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Function.Module.runMain (module.js:497:10)
    at startup (node.js:119:16)
    at node.js:901:3

CoffeeScript Demo

The following terminal commands show a stack trace in node with CoffeeScript filenames:

$ cat > demo.coffee

require('source-map-support').install()
foo = ->
  bar = -> throw new Error 'this is a demo'
  bar()
foo()

$ npm install source-map-support coffee-script
$ node_modules/coffee-script/bin/coffee --map --compile demo.coffee
$ node demo

demo.coffee:4
  bar = -> throw new Error 'this is a demo'
                    ^
Error: this is a demo
    at bar (demo.coffee:4:21)
    at foo (demo.coffee:5:3)
    at Object.<anonymous> (demo.coffee:6)
    at Object.<anonymous> (demo.coffee:2)
    at Module._compile (module.js:449:26)
    at Object.Module._extensions..js (module.js:467:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Module.runMain (module.js:492:10)
    at process.startup.processNextTick.process._tickCallback (node.js:244:9)

TypeScript Demo

The following terminal commands show a stack trace in node with TypeScript filenames:

$ cat > demo.ts

declare function require(name: string);
require('source-map-support').install();
class Foo {
  constructor() { this.bar(); }
  bar() { throw new Error('this is a demo'); }
}
new Foo();

$ npm install source-map-support typescript
$ node_modules/typescript/bin/tsc -sourcemap demo.ts
$ node demo

demo.ts:6
  bar() { throw new Error('this is a demo'); }
               ^
Error: this is a demo
    at Foo.bar (demo.ts:6:16)
    at new Foo (demo.ts:5:23)
    at Object.<anonymous> (demo.ts:8)
    at Module._compile (module.js:449:26)
    at Object.Module._extensions..js (module.js:467:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Module.runMain (module.js:492:10)
    at process.startup.processNextTick.process._tickCallback (node.js:244:9)

Options

This module installs two things: a change to the stack property on Error objects and a handler for uncaught exceptions that mimics node's default exception handler (the handler can be seen in the demos above). You may want to disable the handler if you have your own uncaught exception handler. This can be done by passing an argument to the installer:

require('source-map-support').install({
  handleUncaughtExceptions: false
});

License

This code is available under the MIT license.