Bump to v4.0.0.

isString.js

@@ -0,0 +1,37 @@
+var isArray = require('./isArray'),
+    isObjectLike = require('./isObjectLike');
+
+/** `Object#toString` result references. */
+var stringTag = '[object String]';
+
+/** Used for built-in method references. */
+var objectProto = global.Object.prototype;
+
+/**
+ * Used to resolve the [`toStringTag`](http://ecma-international.org/ecma-262/6.0/#sec-object.prototype.tostring)
+ * of values.
+ */
+var objectToString = objectProto.toString;
+
+/**
+ * Checks if `value` is classified as a `String` primitive or object.
+ *
+ * @static
+ * @memberOf _
+ * @category Lang
+ * @param {*} value The value to check.
+ * @returns {boolean} Returns `true` if `value` is correctly classified, else `false`.
+ * @example
+ *
+ * _.isString('abc');
+ * // => true
+ *
+ * _.isString(1);
+ * // => false
+ */
+function isString(value) {
+  return typeof value == 'string' ||
+    (!isArray(value) && isObjectLike(value) && objectToString.call(value) == stringTag);
+}
+
+module.exports = isString;