fix(options): introduce custom opts.mapper function

resolves #3

README.md

@@ -60,7 +60,7 @@ const stacktraceMetadata = require('stacktrace-metadata')
 
 ## API
 
-### [stacktraceMetadata](index.js#L68)
+### [stacktraceMetadata](index.js#L69)
 > Cleans stack trace and attaches few more metadata properties, such as `at`, `line`, `column`, `filename` and `place`. By default it cleans stack, makes is short (4 length) and makes paths relative. But all this is controllable through `options` object. Throws `TypeError` if `error` is not an instance of Error.
 
 **Params**
@@ -71,6 +71,7 @@ const stacktraceMetadata = require('stacktrace-metadata')
 * `options.shortStack` **{Boolean}**: if `false` full stack traces, otherwise they are just four    
 * `options.showStack` **{Boolean}**: if `false` the error.stack will be empty string    
 * `options.relativePaths` **{Boolean}**: if `false` paths in stack traces will be absolute    
+* `options.mapper` **{Function}**: called on each line of the stack with `(line, index)` signature    
 * `options.cwd` **{String}**: current working directory, default `process.cwd()`    
 * `returns` **{Error}**: same error object, but modified  
 

index.js

@@ -11,7 +11,7 @@ var extend = require('extend-shallow')
 var findCallsite = require('find-callsite')
 var clean = require('clean-stacktrace')
 var metadata = require('clean-stacktrace-metadata')
-var relative = require('clean-stacktrace-relative-paths')
+var relativePaths = require('clean-stacktrace-relative-paths')
 
 /**
  * > Cleans stack trace and attaches few more metadata properties,
@@ -59,6 +59,7 @@ var relative = require('clean-stacktrace-relative-paths')
  * @param  {Boolean} `options.shortStack` if `false` full stack traces, otherwise they are just four
  * @param  {Boolean} `options.showStack` if `false` the error.stack will be empty string
  * @param  {Boolean} `options.relativePaths` if `false` paths in stack traces will be absolute
+ * @param  {Function} `options.mapper` called on each line of the stack with `(line, index)` signature
  * @param  {String} `options.cwd` current working directory, default `process.cwd()`
  * @return {Error} same error object, but modified
  * @throws {TypeError} If `error` not instance of Error
@@ -78,8 +79,10 @@ module.exports = function stacktraceMetadata (error, options) {
       relativePaths: true
     }, options)
 
-    var at = findCallsite(error)
-    at = opts.relativePaths ? relative(opts.cwd)(at) : at
+    var relative = function relative (val) {
+      return opts.relativePaths ? relativePaths(opts.cwd)(val) : val
+    }
+    var at = relative(findCallsite(error))
 
     metadata(function (_, info) {
       error.at = [
@@ -99,8 +102,13 @@ module.exports = function stacktraceMetadata (error, options) {
       error.filename = info.filename
     })(at)
 
-    var mapper = opts.relativePaths ? relative(opts.cwd) : null
-    var stack = clean(error.stack, mapper)
+    var stack = clean(error.stack, function mapper (line, index) {
+      line = typeof opts.mapper === 'function'
+        ? (opts.mapper(line, index) || line)
+        : line
+      line = relative(line)
+      return line
+    })
 
     if (opts.showStack) {
       error.stack = opts.cleanStack ? stack : error.stack

test.js

@@ -173,7 +173,9 @@ test('should work for errors thrown like what rimraf.sync throws', function quxi
   try {
     rimraf.sync(12345)
   } catch (err) {
-    var e = stacktraceMetadata(err)
+    var e = stacktraceMetadata(err, {
+      mapper: function () {}
+    })
 
     test.strictEqual(e.line, 174)
     test.strictEqual(e.column, 12)
@@ -184,3 +186,16 @@ test('should work for errors thrown like what rimraf.sync throws', function quxi
   }
   done()
 })
+
+test('should be able to pass custom opts.mapper function', function (done) {
+  var err = new Error('custom mapper')
+  var e = stacktraceMetadata(err, {
+    mapper: function (line) {
+      test.strictEqual(typeof line, 'string')
+      return line
+    }
+  })
+
+  test.strictEqual(e.stack.trim().length > 0, true)
+  done()
+})