Implement filter, map, and reduce in Javascript

First, implement a foreach function that traverses the array:

 1   Function  Foreach (array, func ){  2           For ( VaR I = 0; I <array. length; I ++ ){  3   Func (array [I]);  4   }  5   }  6   7  Function  Logprint (element ){  8   Console. Log (element );  9   }  10   11 Foreach ([2, 5, 7 ], Logprint );  12   //  Outputs:  13   //  2  14   // 5  15   //  7 

Filter:

 1   Function  Filter (func, array ){  2       VaR Result = [];  3   4 Foreach (array, Function  (Element ){  5               If (Func (element )){  6   Result. Push (element );  7   }  8   });  9   10       Return  Result;  11   }  12   13   Function Gtzero (element ){  14           If (X> 0 ){  15                   Return   True  ;  16   }  17   }  18   19 Filter (gtzero, [3,-2, 0, 5 ]);  20   // [3, 5] 

Map:

 
FunctionMap (func, array ){VaRResult =[]; Foreach (array,Function(Element) {result. Push (func (element ));});ReturnResult ;}FunctionAdd1 (element ){ReturnElement + 1;} Map (Add1 ,[0, 2, 4, 6, 8, 10]);//[1, 3, 5, 7, 9, 11]
 

Reduce:

FunctionReduce (func, init, array) {foreach (array,Function(Element) {init=Func (init, element );});ReturnInit ;}FunctionAdd (element1, element2 ){ReturnElement1 +Element2;} reduce (add,0, [1, 2, 3, 4]);//10
 

The array. Prototype. foreach, array. Prototype. filter, array. Prototype. Map, and other methods are available in the array of ecmascript5,

See http://www.ecma-international.org/ecma-262/5.1/eclipsec-15.4.