improve performance through makePredicate() (#3048)

lib/utils.js

@@ -145,7 +145,7 @@ var MAP = (function(){
             }
             return is_last;
         };
-        if (a instanceof Array) {
+        if (Array.isArray(a)) {
             if (backwards) {
                 for (i = a.length; --i >= 0;) if (doit()) break;
                 ret.reverse();
@@ -210,51 +210,14 @@ function mergeSort(array, cmp) {
     return _ms(array);
 };
 
-// this function is taken from Acorn [1], written by Marijn Haverbeke
-// [1] https://github.com/marijnh/acorn
 function makePredicate(words) {
-    if (!(words instanceof Array)) words = words.split(" ");
-    var f = "", cats = [];
-    out: for (var i = 0; i < words.length; ++i) {
-        for (var j = 0; j < cats.length; ++j)
-            if (cats[j][0].length == words[i].length) {
-                cats[j].push(words[i]);
-                continue out;
-            }
-        cats.push([words[i]]);
-    }
-    function quote(word) {
-        return JSON.stringify(word).replace(/[\u2028\u2029]/g, function(s) {
-            switch (s) {
-                case "\u2028": return "\\u2028";
-                case "\u2029": return "\\u2029";
-            }
-            return s;
-        });
-    }
-    function compareTo(arr) {
-        if (arr.length == 1) return f += "return str === " + quote(arr[0]) + ";";
-        f += "switch(str){";
-        for (var i = 0; i < arr.length; ++i) f += "case " + quote(arr[i]) + ":";
-        f += "return true}return false;";
-    }
-    // When there are more than three length categories, an outer
-    // switch first dispatches on the lengths, to save on comparisons.
-    if (cats.length > 3) {
-        cats.sort(function(a, b) {return b.length - a.length;});
-        f += "switch(str.length){";
-        for (var i = 0; i < cats.length; ++i) {
-            var cat = cats[i];
-            f += "case " + cat[0].length + ":";
-            compareTo(cat);
-        }
-        f += "}";
-        // Otherwise, simply generate a flat `switch` statement.
-    } else {
-        compareTo(words);
-    }
-    return new Function("str", f);
-};
+    if (!Array.isArray(words)) words = words.split(" ");
+    var map = Object.create(null);
+    words.forEach(function(word) {
+        map[word] = true;
+    });
+    return map;
+}
 
 function all(array, predicate) {
     for (var i = array.length; --i >= 0;)