# Thread: [RESOLVED] Function with multiple parameters as parameter

1. Registered User
Join Date
Jul 2013
Posts
16

## [RESOLVED] Function with multiple parameters as parameter

I want to do functional programming in javascript.
Code:
function forEach(array, function)
{
var newArray = new Array();
for(var i=0; i < array.length; i++)
{
newArray[i] = function(this[i]);
}
return newArray;
}
If I have a function like isNumber(x) that returns true if x is a number, then I can use the function written above to apply the isNumber function to an array.
Code:
var arr = [1, 2, "three", 4, "five"];
var boolArr = forEach(arr, isNumber);
//boolArr = [true, true, false, true, false]
But what if I want to apply a function that has multiple parameters? For example sum(a,b) that adds a and b and I would want that function to add all numbers in an array. Or maybe a function like isBetween(x,a,b) that would return true if x is between a and b and I want to be able to do something like forEach(array, isBetween(a,b)) which would check if each element is between a and b. Is there a way to do this?

2. Registered User
Join Date
Jul 2013
Posts
46
sorry i am sort of new to all this but "&&" is and eg
if (A == 1 && B == 1) "this will only run if A == 1 AND B == 1"

also "||" is or eg
if (C == 1 || D == 1) "this will run if C == 1 and/or D == 1"

3. Registered User
Join Date
Mar 2011
Posts
122
A 'forEach' function normally works on the array passed to it. The function you have which returns a new array, is usually called a 'map' function.
Chapter 6 of http://eloquentjavascript.net/ explains some nice tricks on functional programming.

As a way to solve your questions.
Code:
function forEach(array, action){
for(var i=0; i<array.length; i++){
action.call(this, array[i], i);
}
};

function reduce(combine, base, array){
forEach(array,function(element){
base = combine(base ,element);
});
return base;
};

function map(func, array){
var result = [];
forEach(array, function(element, i){
result.push(func(element, i));
});
return result;
};

function asArray(quasiArray, start){
return Array.prototype.splice.call(quasiArray, start)
};

function partial(func) {
var fixedArgs = asArray(arguments, 1);
return function(){
return func.apply(null, fixedArgs.concat(asArray(arguments, 0)));
};
};

return a+b;
};

function isBetween(a, b, x){
return x>a && x<b;
};

var sum = reduce(add, 0, [1,2,3]);
var between = map(partial(isBetween, 3, 7), [1,2,3,4,5,6,7,8,9]);
document.write(sum + '<hr>' +between);