--- /dev/null
+var keys = require('../object/keys');
+
+/**
+ * A specialized version of `_.assign` for customizing assigned values without
+ * support for argument juggling, multiple sources, and `this` binding `customizer`
+ * functions.
+ *
+ * @private
+ * @param {Object} object The destination object.
+ * @param {Object} source The source object.
+ * @param {Function} customizer The function to customize assigned values.
+ * @returns {Object} Returns `object`.
+ */
+function assignWith(object, source, customizer) {
+ var index = -1,
+ props = keys(source),
+ length = props.length;
+
+ while (++index < length) {
+ var key = props[index],
+ value = object[key],
+ result = customizer(value, source[key], key, object, source);
+
+ if ((result === result ? (result !== value) : (value === value)) ||
+ (value === undefined && !(key in object))) {
+ object[key] = result;
+ }
+ }
+ return object;
+}
+
+module.exports = assignWith;