---
id: 5d79253ad297a31cbe073718
title: Part 140
challengeType: 0
dashedName: part-140
---
# --description--
The function in the `map` method can actually take a second argument: the index of the element.
This is why you need an arrow function in `charRange` - if you don't use one, then the index will be passed to `String.fromCharCode` as the second argument, leading to unexpected results. However, it is safe for functions like `parseFloat` which take only one argument (but not for `parseInt`).
Chain `.map((x, i) => x + i)` to `.fill(start)` to add its index to every element in the array in `range`.
# --hints--
See description above for instructions.
```js
assert(
code
.replace(/\s/g, '')
.includes(
'constrange=(start,end)=>Array(end-start+1).fill(start).map((x,i)=>x+i)'
)
);
```
# --seed--
## --before-user-code--
```html
Spreadsheet
```
## --after-user-code--
```html
```
## --seed-contents--
```html
```
# --solutions--
```html
```