flow like the river

VISUALIZACION/node_modules/merge-source-map/index.js

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+var sourceMap = require('source-map')
+var SourceMapConsumer = sourceMap.SourceMapConsumer
+var SourceMapGenerator = sourceMap.SourceMapGenerator
+
+module.exports = merge
+
+/**
+ * Merge old source map and new source map and return merged.
+ * If old or new source map value is falsy, return another one as it is.
+ *
+ * @param {object|string} [oldMap] old source map object
+ * @param {object|string} [newmap] new source map object
+ * @return {object|undefined} merged source map object, or undefined when both old and new source map are undefined
+ */
+function merge(oldMap, newMap) {
+
+  if (!oldMap)
+    return newMap
+  if (!newMap)
+    return oldMap
+
+  var oldMapConsumer = new SourceMapConsumer(oldMap)
+  var newMapConsumer = new SourceMapConsumer(newMap)
+  var mergedMapGenerator = new SourceMapGenerator()
+
+  // iterate on new map and overwrite original position of new map with one of old map
+  newMapConsumer.eachMapping(function(m) {
+
+    // pass when `originalLine` is null.
+    // It occurs in case that the node does not have origin in original code.
+    if (m.originalLine == null)
+      return
+
+    var origPosInOldMap = oldMapConsumer.originalPositionFor({line: m.originalLine, column: m.originalColumn})
+    if (origPosInOldMap.source == null)
+      return
+
+    mergedMapGenerator.addMapping({
+      original: {
+        line: origPosInOldMap.line,
+        column: origPosInOldMap.column
+      },
+      generated: {
+        line: m.generatedLine,
+        column: m.generatedColumn
+      },
+      source: origPosInOldMap.source,
+      name: origPosInOldMap.name
+    })
+  })
+
+  var mergedMap = JSON.parse(mergedMapGenerator.toString())
+
+  mergedMap.sourcesContent = mergedMap.sources.map(function (source) {
+    return oldMapConsumer.sourceContentFor(source)
+  })
+
+  mergedMap.sourceRoot = oldMap.sourceRoot
+
+  return mergedMap
+}