Hey guys,
I'm getting the error message "number is not defined here". Can somebody tell me what I am doing wrong?

Question

In the video about writing callback functions as arrow functions Guil also uses a new undefined argument called movie.
```app.js
const numbers = [1,2,3,4,5,6,7,8,9,10];
let times5 = [];
// times5 should be: [5,10,15,20,25,30,35,40,45,50]
// Write your code below
numbers.forEach(number => number * 5);
times5.push(number);
```

Zimri Leijen · Answer

```js
const numbers = [1,2,3,4,5,6,7,8,9,10];
let times5 = [];
// times5 should be: [5,10,15,20,25,30,35,40,45,50]
// Write your code below
numbers.forEach(number => number * 5); // number is only defined within the scope of this function, and you're not storing it anywhere
times5.push(number); // you're outside the scope of the function here

what you have can be rewritten like this, using traditional functions
js
const numbers = [1,2,3,4,5,6,7,8,9,10];
let times5 = [];
// times5 should be: [5,10,15,20,25,30,35,40,45,50]
// Write your code below
numbers.forEach(function (number) {
   number * 5
});
times5.push(number);
```
what you could do is this
```js
const numbers = [1,2,3,4,5,6,7,8,9,10];
let times5 = [];
// times5 should be: [5,10,15,20,25,30,35,40,45,50]
// Write your code below
numbers.forEach(function (number) {
   times5.push(number*5)
});
```
which would be equivalent of this
```js
const numbers = [1,2,3,4,5,6,7,8,9,10];
let times5 = [];
// times5 should be: [5,10,15,20,25,30,35,40,45,50]
// Write your code below
numbers.forEach(number => times5.push(number*5));
```
even better would be to use the map method, instead of forEach.
```js
const numbers = [1,2,3,4,5,6,7,8,9,10];
// times5 should be: [5,10,15,20,25,30,35,40,45,50]
// Write your code below
const times5 = numbers.map(number => number*5);
```

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Michael Bijnens

Michael Bijnens

Hey guys, I'm getting the error message "number is not defined here". Can somebody tell me what I am doing wrong?

1 Answer

Zimri Leijen

Zimri Leijen