fem-JavaScriptTheHardParts-CallbacksSolutions.js

// Challenge 1
function addTwo(num) {
	return num+2
}

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// Challenge 2
function addS(word) {
	return word + 's'
}

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// Challenge 3
function map(array, callback) {
	let newArr = []
  for (let i=0; i<array.length;i++) {
    newArr[i] = callback(array[i]);
  }
  return newArr
}

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// Challenge 4 //
function forEach(array, callback) {
	for (let i=0; i<array.length;i++) {
    callback(array[i]);
  }
}

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// Extension 1 //
function mapWith(array, callback) {
  let newArr = [];
  forEach(array,function(i) {
    newArr.push(callback(i));
  });
  return newArr;
  }
}

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// Extension 2 //
function reduce(array, callback, initialValue) {
	let total = initialValue; 
  for (let i=0; i<array.length; i++) {
    total = callback(total, array[i]);
  }
  return total;
}

var add = function(a, b) { return a + b; };
var nums = [4, 1, 3];
console.log(reduce(nums,add,0)); 

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// Extension 3 //
function intersection(arrays) {
  //note: 'arguments' is a built-in object corresponding, in this case, to what was passed in for arrays
  let result = [];
  for (let k=1; k < arguments.length-1; k++) { //loops through arrays
    //console.log(arrays[k]);
  	for (let i=0;i<arguments[0].length; i++) { //loops through first array
    		for(let j=0;j<arguments[k].length; j++) { //loops through k'th array
      			if (arguments[0][i] === arguments[k][j]) { //checks if the value is the same as in the first array
        			if (!result.includes(arguments[0][i])) { //checks if number is already noted
          				result.push(arguments[0][i]) //adds the number to our array with elements in all arrays 
        			} 
      			}
    		}
  	}
  }
  return result; 
}

console.log(intersection([5, 10, 15, 20], [15, 88, 1, 5, 7], [1, 10, 15, 5, 20]));
// should log: [5, 15]

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//Extension 4 // 
function union(arrays) {
  //note: 'arguments' is a built-in object corresponding, in this case, to what was passed in for arrays
  let result = []
  for (let i=0; i<arguments.length; i++) {
    for (let j=0; j<arguments[i].length; j++) {
      if (!result.includes(arguments[i][j])) {
        result.push(arguments[i][j]);
      }
    }
  }
  return result
}
console.log(union([5, 10, 15], [15, 88, 1, 5, 7], [100, 15, 10, 1, 5]));
// should log: [5, 10, 15, 88, 1, 7, 100]


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//Extension 5 //
function objOfMatches(array1, array2, callback) {
	let obj = {};
  for (let i=0;i<array1.length;i++) {
  	if (callback(array1[i]) === array2[i]) { //checks if output matches the element
      obj[array1[i]] = array2[i];
  	}
  }
  return obj;
}

console.log(objOfMatches(['hi', 'howdy', 'bye', 'later', 'hello'], ['HI', 'Howdy', 'BYE', 'LATER', 'hello'], function(str) { return str.toUpperCase(); }));
// should log: { hi: 'HI', bye: 'BYE', later: 'LATER' }

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//Extension 6 //

function multiMap(arrVals, arrCallbacks) {
	let obj = {};
  	for (let i=0; i<arrVals.length; i++) {
    		let result = [];
    		for (let j=0; j<arrCallbacks.length; j++) {
      			let currCb = arrCallbacks[j];
      			result.push(currCb(arrVals[i]));
    		}
    		obj[arrVals[i]] = result; 
  	}
  	return obj;
}

console.log(multiMap(['catfood', 'glue', 'beer'], [function(str) { return str.toUpperCase(); }, function(str) { return str[0].toUpperCase() + str.slice(1).toLowerCase(); }, function(str) { return str + str; }]));
// should log: { catfood: ['CATFOOD', 'Catfood', 'catfoodcatfood'], glue: ['GLUE', 'Glue', 'glueglue'], beer: ['BEER', 'Beer', 'beerbeer'] }