perf: use === for placeholder test (#3388)

source/__.js

@@ -1,3 +1,4 @@
+import _placeholder from './internal/_placeholder.js';
 /**
  * A special placeholder value used to specify "gaps" within curried functions,
  * allowing partial application of any combination of arguments, regardless of
@@ -25,4 +26,4 @@
  *      const greet = R.replace('{name}', R.__, 'Hello, {name}!');
  *      greet('Alice'); //=> 'Hello, Alice!'
  */
-export default {'@@functional/placeholder': true};
+export default _placeholder;

source/internal/_isPlaceholder.js

@@ -1,5 +1,5 @@
+import _placeholder from './_placeholder.js';
+
 export default function _isPlaceholder(a) {
-  return a != null &&
-         typeof a === 'object' &&
-         a['@@functional/placeholder'] === true;
+  return a === _placeholder;
 }

source/internal/_placeholder.js

@@ -0,0 +1 @@
+export default {'@@functional/placeholder': true};

test/curry.js

@@ -78,7 +78,7 @@ describe('curry', function() {
   it('supports @@functional/placeholder', function() {
     var f = function(a, b, c) { return [a, b, c]; };
     var g = R.curry(f);
-    var _ = {'@@functional/placeholder': true, x: Math.random()};
+    var _ = R.__;
 
     eq(g(1)(2)(3), [1, 2, 3]);
     eq(g(1)(2, 3), [1, 2, 3]);
@@ -167,7 +167,7 @@ describe('curry properties', function() {
 
   it('curries with placeholder', function() {
     fc.assert(fc.property(fc.func(fc.anything()), fc.anything(), fc.anything(), fc.anything(), function(f, a, b, c) {
-      var _ = {'@@functional/placeholder': true, x: Math.random()};
+      var _ = R.__;
       var f3 = function(a, b, c) {
         return f(a, b, c);
       };

test/curryN.js

@@ -67,7 +67,7 @@ describe('curryN', function() {
   it('supports @@functional/placeholder', function() {
     var f = function() { return Array.prototype.slice.call(arguments); };
     var g = R.curryN(3, f);
-    var _ = {'@@functional/placeholder': true, x: Math.random()};
+    var _ = R.__;
 
     eq(g(1)(2)(3), [1, 2, 3]);
     eq(g(1)(2, 3), [1, 2, 3]);