Javascript array map, reduce practice

js-array-practice.js

// 1. Implement `reduce` via forEach. Expected api for the function:
reduce(arr, (acc, item) => acc + item, 0);

// example of implementation:
function reduce(arr, reducerCallback, initialValue) {
  let result;
  ……forEach(…)
  return result;
}

// 2. Implement `map` via reduce
map([…], (item) => item + 1);

// 3. Implement `filter` via reduce
filter([…], (item) => item === 1);

// 4. Implement `some` and `every` via reduce
some([…], (item) => item === 1);
every([…], (item) => item === 1);

// 5. Implement `find` via reduce
find([…], (item) => item === 1);

/**
* 6. Functional Programming in Javascript
* @link http://reactivex.io/learnrx/
*/

/**
* 7. Quick JavaScript Array Functions Practice
* @link https://github.com/jamesqquick/javascript-array-functions-practice
*/

/**
* 8. Practicing Arrays, ForEach, Map, Filter and Reduce
* @link https://gist.github.com/tgmarinho/f1a145d7c7c87fc495181ba21cf3681f
*/


// Simple problems to solve using the native .reduce and .map array methods. Each of these problems can be solved in many
// different ways, but try to solve them using the requested higher order function.

// MAP

// Write a function capitalize that takes a string and uses .map to return the same string in all caps. 
// ex. capitalize('whoop') // => 'WHOOP'
// ex. capitalize('oh hey gurl') // => "OH HEY GURL"
var capitalize = function(string){
  // code code code!
}

// Now write a new function called swapCase that takes a string of words and uses .map and your newly written capitalize() 
// function to return a string where every other word is in all caps. 
// Hint: look up Array.prototype.map on MDN and see what arguments the .map callback can take. 
// ex: swapCase('hey gurl, lets javascript together sometime') // => "HEY gurl, LETS javascript TOGETHER sometime"
var swapCase = function(string){
  // Codeeeee
}

// Write a function shiftLetters that takes a string and uses .map to return an encoded string with each letter shifted down the 
// alphabet by one. Hint: Use Look up the JS functions String.fromCharCode() and String.CharCodeAt() and see if you can use
// Ascii code to acomplish this.
// ex. shiftLetters('hello') // => 'ifmmp'
// ex. (shiftLetters('abcxyz') // => "bcdyz{"
var shiftLetters = function(string){
  // code!
}

// REDUCE

// Write a function that takes a string and returns an object representing the character 
// count for each letter. Use .reduce to build this object. 
// ex. countLetters('abbcccddddeeeee') // => {a:1, b:2, c:3, d:4, e:5}
var countLetters = function(string){
  // your code here
};

// Write a function that takes a string and a target, and returns true or false if the target is present in the string. Use
// .reduce to acomplish this.
// ex. isPresent('abcd', 'b') // => true
// ex. isPresent('efghi', 'a') // => false
var isPresent = function(string, target) {
  // GO GO GADGET CODE!
}