Array.Reduce()

Question 1

const array1 = [1, 2, 3, 4];
const reducer = 

console.log(array1.reduce(reducer));
// 1 + 2 + 3 + 4

Answer 1

(accumulator, currentValue) => accumulator + currentValue;

Question 2

const array1 = [1, 2, 3, 4];
const reducer = 

console.log(array1.reduce(reducer, 5));

Answer 2

const reducer = (accumulator, currentValue) => accumulator + currentValue;

Question 3

The reducer function takes four arguments:

1.
2.
3.
4.

Answer 3

Accumulator (acc)
Current Value (cur)
Current Index (idx)
Source Array (src)

Question 4

arr.reduce(_____(_____, _______[, index[, array]]), [, initialValue])

Answer 4

callback Function
accumulator
Current Value

Question 5

The __________ adds the callback’s return values. It is the added value previously returned in the last invocation of the callback, or initialValue, if supplied (see below)

Answer 5

accumulator

Question 6

The current element being processed in the array.

Answer 6

currentValue

Question 7

the 3 optional values are:

Answer 7

currentIndex
array
initialValue

Question 8

The current element being processed in the array.

Answer 8

currentValue

Question 9

The index of the current element being processed in the array. Starts from index 0 if an initialValue is provided. Otherwise, starts from index 1.

Answer 9

currentIndex

Question 10

A value to use as the first argument to the first call of the callback. If no initialValue is supplied, the first element in the array will be used. Calling reduce() on an empty array without an initialValue will throw a TypeError.

Answer 10

initialValue

Question 11

The first time the callback is called, _________ and __________ can be one of two values.

Answer 11

accumulator

currentValue

Question 12

If initialValue is not provided, reduce() will execute the callback function starting at __________ skipping the first index. If initialValue is provided, it will start at _______

Answer 12

index 1

index 0

Question 13

var sum = [0, 1, 2, 3].reduce( 
// code here
)
// sum is 6

Answer 13

function (accumulator, currentValue) {
  return accumulator + currentValue;
}

Question 14

var total = [ 0, 1, 2, 3 ].reduce(
// code here
);

Answer 14

( accumulator, currentValue ) => accumulator + currentValue

Question 15

To sum up the values contained in an array of objects, you must supply an_________, so that each item passes through your function.

Answer 15

initialValue

Question 16

var sum = [{x: 1}, {x: 2}, {x: 3}].reduce(function (accumulator, currentValue) {
    return \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
},0)

console.log(sum) // logs 6

Answer 16

accumulator + currentValue.x;

Question 17

var initialValue = 0;
var sum = [{x: 1}, {x: 2}, {x: 3}].reduce(function (accumulator, currentValue) {
    return accumulator + currentValue.x;
},initialValue)

WRITE AS A ARROW FUNCTION

Answer 17

( (accumulator, currentValue) => accumulator + currentValue.x
,initialValue
);

Question 18

var flattened = [[0, 1], [2, 3], [4, 5]].reduce(accumulator, currentValue =>

);
// flattened is [0, 1, 2, 3, 4, 5]

Answer 18

accumulator.concat(currentValue);

Question 19

If you are using an environment compatible with Set and Array.from(), you could use

let orderedArray = // ->?

to get an array where duplicate items have been removed.

Answer 19

Array.from(new Set(myArray));

Question 20

const array1 = [[0, 1], [2, 3], [4, 5]].____________(
(accumulator, currentValue) => accumulator.concat(currentValue)
);

console.log(array1);
// expected output: Array [4, 5, 2, 3, 0, 1]

Answer 20

reduceRight

Question 21

arr.reduce(callback(accumulator, currentValue[, _______[,______]]), [,________])

Answer 21

index
array
initial value

Question 22

you use intiliaze a object with reduce by adding

Answer 22

comma with braces to the end of the function

Question 23

what’s is this missing

var flattened = [[0, 1], [2, 3], [4, 5]].reduce(
  function(accumulator, currentValue) {
    return accumulator.concat(currentValue);
  },

);

Answer 23

array brackets at end

Question 24

Calling reduce() on an empty array without an initialValue will __________

Answer 24

throw a TypeError.

Question 25

[ ].reduce( maxCallback ); //

Answer 25

TypeError

Question 26

_______ will increment the value of i, and then return the incremented value.

Answer 26

++i

Question 27

________ will increment the value of i, but return the original value that i held before being incremented.

Answer 27

i++

Question 28

i = 1;
j = ++i;
(i is ___, j is _____)

Answer 28

2

2

Question 29

i = 1;
j = i++;
(i is ____, j is _____)

Answer 29

2

1

Question 30

const array1 = [1, 2, 3, 4];
const reducer = (accumulator, currentValue) => accumulator + currentValue;

console.log(array1.reduce(reducer));
// expected output:

Answer 30

10

Question 31

const array1 = [1, 2, 3, 4];
const reducer = (accumulator, currentValue) => accumulator + currentValue;

// 1 + 2 + 3 + 4
console.log(\_\_\_\_\_\_\_\_\_\_\_\_\_);
// To get expected output of 10

Answer 31

array1.reduce(reducer)

Question 32

Sum all the values of an array using arrow

var sum = [0, 1, 2, 3]

// sum is 6

Answer 32

reduce(
( accumulator, currentValue ) => accumulator + currentValue,
0 );

Question 33

Sum all the values of an array using function

var sum = [0, 1, 2, 3]

// sum is 6

Answer 33

.reduce(function (accumulator, currentValue) {
return accumulator + currentValue;
}, 0);

Question 34

const array1 = [[0, 1], [2, 3], [4, 5]].reduceRight(

CODE HERE

console.log(array1);
// expected output: Array [5, 4, 2, 3, 0, 1]

Answer 34

(accumulator, currentValue) => accumulator.concat(currentValue)
);

Question 35

The _____________ method applies a function against an accumulator and each value of the array (from right-to-left) to reduce it to a single value.

Answer 35

reduceRight()

Question 36

The __________ method executes a reducer function (that you provide) on each element of the array, resulting in a single output value.

Answer 36

reducer

Question 37

let arr = [1, 2, 3, 4, 5];

add all numbers in array
let result =

alert(result); // 15

Answer 37

arr.reduce((sum, current) => sum + current, 0);

Question 38

let value = arr.reduce(function(\_\_\_,\_\_\_,\_\_\_\_\_,\_\_\_\_\_\_) {
  // ...
}, initial);

Answer 38

previousValue, item, index, array

Question 39

WHAT CAN BE REMOVED AND WHY

let arr = [1, 2, 3, 4, 5];

let result = arr.reduce((sum, current) => sum + current, 0);

alert(result); // 15

Answer 39

0

current value at 0

Question 40

const numbers = [5, 10, 15];
const total = numbers.reduce( (accumulator, currentValue) => accumulator + currentValue, 44);

console.log(total);

Answer 40

74

30 from function + the 44 start point

Question 41

var a = ['1', '2', '3', '4', '5']; 
var left  = a.reduce

console.log(left); // “12345”

Answer 41

(function(prev, cur) { return prev + cur; });

Question 42

var a = [‘1’, ‘2’, ‘3’, ‘4’, ‘5’];

var right = a.reduceRight

console.log(right); // “54321”

Answer 42

(function(prev, cur) { return prev + cur; });

Question 43

the _____ doesn’t have to be used to accumulate a number rather it can be used to return the higest price.

Answer 43

accumulator

Question 44

const products = [
  { name: 'hard drive', price: 59.99 },
  { name: 'lighbulbs', price: 2.59 },
  { name: 'paper towels', price: 6.99 },
  { name: 'flatscreen monitor', price: 159.99 },
  { name: 'cable ties', price: 19.99 },
  { name: 'ballpoint pens', price: 4.49 }
];

Answer 44

const product = products
  .filter(product => product.price < 10)
  .reduce((highest, product) => {
    if (highest.price > product.price) {
      return highest;
    }
    return product;
  }, { price: 0 });