Modularize master branch.

isLength.js

@@ -0,0 +1,35 @@
+/** Used as references for various `Number` constants. */
+var MAX_SAFE_INTEGER = 9007199254740991;
+
+/**
+ * Checks if `value` is a valid array-like length.
+ *
+ * **Note:** This method is loosely based on
+ * [`ToLength`](http://ecma-international.org/ecma-262/7.0/#sec-tolength).
+ *
+ * @static
+ * @memberOf _
+ * @since 4.0.0
+ * @category Lang
+ * @param {*} value The value to check.
+ * @returns {boolean} Returns `true` if `value` is a valid length, else `false`.
+ * @example
+ *
+ * _.isLength(3);
+ * // => true
+ *
+ * _.isLength(Number.MIN_VALUE);
+ * // => false
+ *
+ * _.isLength(Infinity);
+ * // => false
+ *
+ * _.isLength('3');
+ * // => false
+ */
+function isLength(value) {
+  return typeof value == 'number' &&
+    value > -1 && value % 1 == 0 && value <= MAX_SAFE_INTEGER;
+}
+
+export default isLength;