added unit testing, and started implementing unit tests...phew

node_modules/lodash/isSafeInteger.js

@@ -0,0 +1,37 @@
+var isInteger = require('./isInteger');
+
+/** Used as references for various `Number` constants. */
+var MAX_SAFE_INTEGER = 9007199254740991;
+
+/**
+ * Checks if `value` is a safe integer. An integer is safe if it's an IEEE-754
+ * double precision number which isn't the result of a rounded unsafe integer.
+ *
+ * **Note:** This method is based on
+ * [`Number.isSafeInteger`](https://mdn.io/Number/isSafeInteger).
+ *
+ * @static
+ * @memberOf _
+ * @since 4.0.0
+ * @category Lang
+ * @param {*} value The value to check.
+ * @returns {boolean} Returns `true` if `value` is a safe integer, else `false`.
+ * @example
+ *
+ * _.isSafeInteger(3);
+ * // => true
+ *
+ * _.isSafeInteger(Number.MIN_VALUE);
+ * // => false
+ *
+ * _.isSafeInteger(Infinity);
+ * // => false
+ *
+ * _.isSafeInteger('3');
+ * // => false
+ */
+function isSafeInteger(value) {
+  return isInteger(value) && value >= -MAX_SAFE_INTEGER && value <= MAX_SAFE_INTEGER;
+}
+
+module.exports = isSafeInteger;