Replace some _.isFunction checks with simple typeof checks and replace some typeof checks with _.isFunction checks based on likelihood of a problem value older enviros being passed.

lodash.src.js

@@ -1907,7 +1907,7 @@
      * @returns {number} Returns the timer id.
      */
     function baseDelay(func, wait, args, fromIndex) {
-      if (!isFunction(func)) {
+      if (typeof func != 'function') {
         throw new TypeError(FUNC_ERROR_TEXT);
       }
       return setTimeout(function() { func.apply(undefined, baseSlice(args, fromIndex)); }, wait);
@@ -3331,7 +3331,7 @@
      */
     function createWrapper(func, bitmask, thisArg, partials, holders, argPos, ary, arity) {
       var isBindKey = bitmask & BIND_KEY_FLAG;
-      if (!isBindKey && !isFunction(func)) {
+      if (!isBindKey && typeof func != 'function') {
         throw new TypeError(FUNC_ERROR_TEXT);
       }
       var length = partials ? partials.length : 0;
@@ -6655,8 +6655,8 @@
      * // => logs 'done saving!' after the two async saves have completed
      */
     function after(n, func) {
-      if (!isFunction(func)) {
+      if (typeof func != 'function') {
-        if (isFunction(n)) {
+        if (typeof n == 'function') {
           var temp = n;
           n = func;
           func = temp;
@@ -6714,8 +6714,8 @@
      */
     function before(n, func) {
       var result;
-      if (!isFunction(func)) {
+      if (typeof func != 'function') {
-        if (isFunction(n)) {
+        if (typeof n == 'function') {
           var temp = n;
           n = func;
           func = temp;
@@ -7037,7 +7037,7 @@
           maxWait = false,
           trailing = true;
 
-      if (!isFunction(func)) {
+      if (typeof func != 'function') {
         throw new TypeError(FUNC_ERROR_TEXT);
       }
       wait = wait < 0 ? 0 : wait;
@@ -7322,7 +7322,7 @@
      * // => { 'user': 'barney' }
      */
     function memoize(func, resolver) {
-      if (!isFunction(func) || (resolver && !isFunction(resolver))) {
+      if (typeof func != 'function' || (resolver && typeof resolver != 'function')) {
         throw new TypeError(FUNC_ERROR_TEXT);
       }
       var memoized = function() {
@@ -7360,7 +7360,7 @@
      * // => [1, 3, 5]
      */
     function negate(predicate) {
-      if (!isFunction(predicate)) {
+      if (typeof predicate != 'function') {
         throw new TypeError(FUNC_ERROR_TEXT);
       }
       return function() {
@@ -7540,7 +7540,7 @@
       var leading = true,
           trailing = true;
 
-      if (!isFunction(func)) {
+      if (typeof func != 'function') {
         throw new TypeError(FUNC_ERROR_TEXT);
       }
       if (options === false) {
@@ -8818,12 +8818,12 @@
 
       var Ctor = object.constructor,
           index = -1,
-          proto = (typeof Ctor == 'function' && Ctor.prototype) || objectProto,
+          proto = (isFunction(Ctor) && Ctor.prototype) || objectProto,
           isProto = proto === object,
           result = Array(length),
           skipIndexes = length > 0,
           skipErrorProps = support.enumErrorProps && (object === errorProto || object instanceof Error),
-          skipProto = support.enumPrototypes && typeof object == 'function';
+          skipProto = support.enumPrototypes && isFunction(object);
 
       while (++index < length) {
         result[index] = (index + '');
@@ -9137,7 +9137,7 @@
           if (isArr) {
             accumulator = isArray(object) ? new Ctor : [];
           } else {
-            accumulator = baseCreate(typeof Ctor == 'function' && Ctor.prototype);
+            accumulator = baseCreate(isFunction(Ctor) && Ctor.prototype);
           }
         } else {
           accumulator = {};