Javascript function call with another function as parameter

Question

I have a few functions in two different files that are all linked together by function calls they are as follows

FILE 1:

function getFunction(func){
} 

FILE 2:

function Numbers(one, two) {
 return (one*two);
}
var func = getFunction(Numbers);

and these are called by:

func(input_array);

my array has values 1,3,5,7,9 and I need func(input_array) to return 3,15,35,63,9 (the last value loops back to the first value)

basically what I am trying to do is have getFunction return a function such that these values are calculated. I am having trouble because I can't wrap my mind about sending and returning functions. I don't know how to access the array if it isn't sent into the function. Let me know if I need to clarify anything.

• Brad: var func = getFunction(Numbers)... why not var func = Numbers? I don't understand at all what it is that you're trying to do. You can assign functions to variables, just like any other value. You can return functions from other functions. You can use anonymous functions.
• Barmar: @Brad He wants to know what to put into getFunction so it returns a higher-order function that performs the loop that he wants.
• Dimag Kharab: You can use like this -- > var getFunction = function(Numbers){ //your code }

Answer 1

function getFunction(callback) {
 return function(array) {
 return array.map(function(cur, index) {
 return callback(cur, array[(index+1) % array.length]);
 });
 };
}

getFunction returns a closure over the callback parameter, which is the function that you want to call. The closure receives the array parameter, and it calls the callback in a loop over the array using array.map. The % modulus operator performs the wraparound that you want.

Another way to write this that may be clearer is:

function getFunction(callback) {
 return function(array) {
 var result = [];
 for (var i = 0; i < array.length; i++) {
 j = (i+1) % array.length; // Next index, wrapping around
 result.push(callback(array[i], array[j]));
 }
 return result;
 };
}
var func = getFunction(Numbers);
console.log(func([1,3,5,7,9])); // Logs [3,15,35,63,9]

• cwendel: Fixed the function variable name to func. Would you mind explaining what you are doing here?
• Barmar: I added an explanation a minute ago.
• Barmar: I've added another version that uses an explicit loop instead of array.map, it may make the logic clearer.
• Oleksandr T.: Good examples, however in first example you always use array.length I think this bad for performance, this is my opinion, What do you think about it ?
• Barmar: I don't think there's any performance hit. It doesn't have to count the elements, it's a property of the array.

Answer 2

here is simple function that returns what you need

function Numbers(x) { 
 output_array=[];
 for(i=0;i<x.length;i++){ 
 if(x[i+1]==undefined){
 output_array.push(x[i]);
 }
 else{
 output_array.push(x[i]*x[i+1]);
 }
 }
 return output_array;
}
var input_array=[1,3,5,7];
var num = Numbers(input_array);
console.log(num);

OR if you need it in the way function calling another function and than returning the result use this

function getFunction(Numbers,input_array){
 return Numbers(input_array);
}
function Numbers(x) { 
 output_array=[];
 for(i=0;i<x.length;i++){
 if(x[i+1]==undefined){
 output_array.push(x[i]);
 }
 else{
 output_array.push(x[i]*x[i+1]);
 }
 }
 return output_array;
}
var input_array=[1,3,5,7];
var num = getFunction(Numbers,input_array);
console.log(num);