Today I found myself needing to brush up on some functional programming concepts in JavaScript, namely the map(), filter(), and reduce() array methods. I found a good primer and went through the examples.

Map Operation

  • used to modify the input set of array values into another output array
  • does not change the values of the input array
  • map function should only modify the input parameter - should not modify values outside of the map function
var namesMapMethod ={
    return name.toUpperCase();

additionally, you can change multiple .map() functions together

var namesChained ={
    return name.toUpperCase();
    return name.replace('A', '@'); 

Filter Operation

  • used to return a subset of array values from the input array
  • does not modify the input array
  • should not modify any values outside of the filter function
var filtered = names.filter(function(name){
    return (name.indexOf('a') > -1);

Reduce Operation

  • takes an input array and returns a scalar result (unless you define the result as an array)
  • can be used for string concatenation, calculating totals, etc.
var nameString = names.reduce(function(result, name){
    return result + name + "-";
}, "");


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