Verify your source map mappings locally

readSourceMap.js

/* npm install -g source-map */

var fs = require('fs');

var sourceMap = require('source-map');
var rawSourceMap = fs.readFileSync('./app.js.map').toString();
var smc = new sourceMap.SourceMapConsumer(rawSourceMap);

// output original filename, line, column, token for input {line, column}
// in built/minified file (e.g. app.min.js)
// see: https://github.com/mozilla/source-map#sourcemapconsumerprototypeoriginalpositionforgeneratedposition
var pos = smc.originalPositionFor({ line: 1337, column: 1337});

// should see something like:
// { source: 'original.js', line: 1, column: 9, name: 'test' }
console.log(pos);