Arrays – reduce()
Name:
Date:
Class:
A
Quick Questions
Shade in the A or B circle for each question.
1. Does reduce() combine all elements into a single value?
2. Does reduce() return a new array like map() does?
3. Is a return statement needed inside reduce()'s function?
4. Can reduce() take a starting value as a second argument?
5. Is 'Reduce' with a capital R valid JavaScript syntax?
B
Match the Pairs
Draw a line connecting each item on the left to its match on the right.
| Left column | Right column | |
|---|---|---|
| 1nums.reduce(function(total, n) { return total + n; }, 0) | AMultiplies every number in nums into a single product | |
| 2nums.reduce(function(total, n) { return total * n; }, 1) | BAdds up every number in nums into a single total | |
| 3Combines every element into a single result value | CWrong - 'reduce' must start with a lowercase r | |
| 4Sets the accumulator's value before the loop begins | DWrong - missing the 'return' keyword | |
| 5nums.Reduce(function(t, n) { return t+n; }, 0) | E0 | |
| 6nums.reduce(function(t, n) { t + n; }, 0) | Farray.reduce(function(total, item) { ... }) |
C
Definitions
reduce()
D
Fill in the Blanks
Complete each line of code by filling in the missing parts.
1.
let sum = nums.______(function(total, n) {
2.
let sum = nums.reduce(________(total, n) {
3.
______ total + n;
4.
let product = nums.______
(function(total, n) {
5.
let product = nums.reduce(function(total, n)
{
______ total * n;
}, 1);
E
Spot the Error
Shade in the letter of the line that contains an error.
Question 1
A
let a = [1, 2, 3];
B
let b = a.Reduce(function(t, n) {
C
return t + n;
Question 2
A
let c = [1, 2, 3];
B
let d = c.reduce(function(t, n) {
C
t + n;
Question 3
A
let e = [1, 2, 3];
B
let f = e.map(function(t, n) {
C
return t + n;
Question 4
A
let g = [1, 2, 3];
B
let h = g.reduce(function(t, n) {
C
return t + n
D
}, 0);
Question 5
A
let i = [1, 2, 3];
B
let j = i.reduce(function(t, n) {
C
return t + n;
D
], 0);
Answer Key
Arrays – reduce()
Section A: Quick Questions
Q1
A — Yes
Q2
A — No
Q3
B — Yes
Q4
B — Yes
Q5
A — No
Section B: Match the Pairs
Q1
nums.reduce(function(total, n) { return total + n; }, 0) → Adds up every number in nums into a single total
Q2
nums.reduce(function(total, n) { return total * n; }, 1) → Multiplies every number in nums into a single product
Q3
Combines every element into a single result value → array.reduce(function(total, item) { ... })
Q4
Sets the accumulator's value before the loop begins → 0
Q5
nums.Reduce(function(t, n) { return t+n; }, 0) → Wrong - 'reduce' must start with a lowercase r
Q6
nums.reduce(function(t, n) { t + n; }, 0) → Wrong - missing the 'return' keyword
Section C: Definitions
Q1
reduce() — Combines every element of an array into a single value using an accumulator function.Section D: Fill in the Blanks
Q1
let sum = nums.reduce(function(total, n) {Q2
let sum = nums.reduce(function(total, n) {Q3
return total + n;Q4
let product = nums.reduce
(function(total, n) {Q5
let product = nums.reduce(function(total, n)
{
return total * n;
}, 1);Section E: Spot the Error
Q1
B — 'reduce' must start lowercase - a capital R causes an error.
Q2
C — Missing the 'return' keyword - without it, nothing is carried forward.
Q3
B — map() doesn't combine values into one - use reduce() instead.
Q4
C — This line is missing a semicolon, but that's not required in JS.
Q5
D — The block must close with }, not ].