Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

JavaScript JavaScript Array Iteration Methods Array Iteration Practice forEach()

Dan Smith
Dan Smith
2,942 Points
Posted by Dan Smith
Dan Smith
2,942 Points

How can i determine which part of the array i want to multiply and how do i send it to a new var?

const numbers = [1,2,3,4,5,6,7,8,9,10]; let times10 = [];

// times10 should be: [10,20,30,40,50,60,70,80,90,100] // Write your code below

//Your Code Goes Here: numbers.forEach(function(multiply) { multiply [i] = ""; return times10 = (multiply[i] *= 10); });

I CANNOT FIGURE HOW CAN I TELL THE JS THAT I WANT TO MULTIPLE THE CONST NUMBERS.

app.js 
const numbers = [1,2,3,4,5,6,7,8,9,10];
let times10 = [];


// times10 should be: [10,20,30,40,50,60,70,80,90,100]
// Write your code below

numbers.forEach(function(multiply) {
multiply [i] = "";
  return times10 = (multiply[i] *= 10);
});

3 Answers

Gabbie Metheny
Gabbie Metheny
33,778 Points
Gabbie Metheny
Gabbie Metheny
33,778 Points

With .forEach(), you don't need to worry about a counter variable, it's build into the method! So there's no need for an index of [i] in your code. I'd also recommend changing your multiply parameter to number, simply because it will hopefully clarify what is happening in your code - you're iterating over each number in numbers.

Right now, you're trying to return the number you've multiplied, but you want to actually add it to the array. You can use the .push() method for this. 

numbers.forEach(function(number) {
  // multiply the number by 10 
  // and push it onto the times10 array
});

Let me know if you need further clarification!

Dan Smith
Dan Smith
2,942 Points
Dan Smith
Dan Smith
2,942 Points

so it basically knows i want to use all the items inside the array? what if i have a chain of arrays?

Gabbie Metheny
Gabbie Metheny
33,778 Points
Gabbie Metheny
Gabbie Metheny
33,778 Points

Yes, it's basically a shortcut if you want to do something to each item in an array.

const array = [1, 2, 3, 4];
for (let i=0; i<array.length; i+=1 ) {
  console.log(array[i])
}
// output:
// 1
// 2
// 3
// 4

const array = [1, 2, 3, 4];
array.forEach(function(number) {
  console.log(number);
});
// output:
// 1
// 2
// 3
// 4

The above two loops will produce the same output.

As far as a chain of arrays, can you give me an example of what you mean?

Thomas Nilsen
Thomas Nilsen
14,957 Points
Thomas Nilsen
Thomas Nilsen
14,957 Points

You could use the map-function for this:

const numbers = [1,2,3,4,5,6,7,8,9,10];
let times10 = [];


// times10 should be: [10,20,30,40,50,60,70,80,90,100]
// Write your code below

times10 = numbers.map(n => n * 10)
console.log(times10);

Edit

Sorry - I didn't see this was a forEach challenge. I'll just leave the answer here if you're interested