add book.js

node_modules/lodash/internal/baseSum.js

@@ -0,0 +1,20 @@
+var baseEach = require('./baseEach');
+
+/**
+ * The base implementation of `_.sum` without support for callback shorthands
+ * and `this` binding.
+ *
+ * @private
+ * @param {Array|Object|string} collection The collection to iterate over.
+ * @param {Function} iteratee The function invoked per iteration.
+ * @returns {number} Returns the sum.
+ */
+function baseSum(collection, iteratee) {
+  var result = 0;
+  baseEach(collection, function(value, index, collection) {
+    result += +iteratee(value, index, collection) || 0;
+  });
+  return result;
+}
+
+module.exports = baseSum;