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---
id: 5ddb965c65d27e1512d44dad
title: Part 20
challengeType: 0
---
## Description
< section id = 'description' >
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Let's says we have an array `[1, 3, 5]` named `arr` and we want to sum up all the numbers.
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We can use the reduce function as follows:
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```js
arr.reduce((accumulator, currentValue) => {
return accumulator + currentValue;
}, 0);
```
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At `arr[0]` , the function is `(0, 1) => { return 0 + 1 }` ,
since `arr[0] = 1 = currentValue` .
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At `arr[1]` , the function is `(1, 3) => 1 + 3` ,
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Finally at `arr[2]` , the function is `(4, 5) => 4 + 5` . Now the accumulator is `9` and since we have gone through all of the items in `arr` , the `reduce()` method will return `9` .
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In the body of the callback function, replace `/* code to run */` with `return accumulator + currentValue` .
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< / section >
## Instructions
< section id = 'instructions' >
< / section >
## Tests
< section id = 'tests' >
```yml
tests:
- text: See description above for instructions.
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testString: assert( code.replace(/\s/g, '').match(/reduce\(\(accumulator\,currentValue\)\=\>{returnaccumulator\+currentValue\;?},0\)/) );
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```
< / section >
## Challenge Seed
< section id = 'challengeSeed' >
< div id = 'html-seed' >
```html
< script >
document.getElementById('calorie-form').onsubmit = calculate;
function calculate(e) {
e.preventDefault();
const total = Array.from(document.getElementsByClassName('cal-control'))
.map(meal => Number(meal.value))
.reduce((accumulator, currentValue) => {
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/* code to run */
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}, 0);
}
< / script >
```
< / div >
### Before Test
< div id = 'html-setup' >
```html
<!DOCTYPE html>
< html >
< head >
< meta charset = "utf-8" / >
< title > < / title >
< meta name = "description" content = "" / >
< meta name = "viewport" content = "width=device-width, initial-scale=1" / >
< link rel = "stylesheet" href = "styles.css" / >
< / head >
< body >
< div class = "container" >
< form id = "calorie-form" >
< h2 class = "center" > Calorie Counter< / h2 >
< div class = "grid" >
< legend > Sex< / legend >
< div >
< input type = "radio" name = "sex" id = "female" value = "F" checked / >
< label for = "female" >
Female (2,000 calories)
< / label >
< div >
< input type = "radio" name = "sex" id = "male" value = "M" / >
< label for = "male" >
Male (2,500 calories)
< / label >
< / div >
< / div >
< / div >
< div class = "grid" id = "entries" >
Breakfast
< input
type="number"
min="0"
class="cal-control"
id="breakfast"
/>< br / >
Lunch
< input type = "number" min = "0" class = "cal-control" id = "lunch" / > < br / >
Dinner < input type = "number" min = "0" class = "cal-control" id = "dinner" / >
< / div >
< button type = "button" class = "btn-add" id = "add" >
Add Entry
< / button >
< button type = "submit" class = "btn-solid" id = "calculate" >
Calculate
< / button >
< button type = "button" class = "btn-outline" id = "clear" >
Clear
< / button >
< / form >
< div id = "output" > < / div >
< / div >
< / body >
< / html >
```
< / div >
### After Test
< div id = 'html-teardown' >
```html
< / body >
< / html >
```
< / div >
< / section >
## Solution
< section id = 'solution' >
```html
< script >
document.getElementById('calorie-form').onsubmit = calculate;
function calculate(e) {
e.preventDefault();
const total = Array.from(document.getElementsByClassName('cal-control'))
.map(meal => Number(meal.value))
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.reduce((accumulator, currentValue) => {
return accumulator + currentValue;
}, 0);
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}
< / script >
```
< / section >
