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 Manipulation Practice map()

Posted by Christopher Evans
Christopher Evans
9,896 Points

Cannot read property '2' of undefined.

Don't understand why anything would be undefined here...

app.js 
const daysOfWeek = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"];
let abbreviatedDays;

// abbreviatedDays should be: ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"]
// Write your code below
abbreviatedDays = daysOfWeek.map((day) => day[0][1][2]);

1 Answer

Steven Parker
Steven Parker
231,272 Points
Steven Parker
Steven Parker
231,272 Points

The expression "day[0][1][2]" would be a way to index into a 3-dimensional array. But "day" represents a single string from the "daysOfWeek" array. So the first index will refer to a single character, and the next one will be "undefined" (and the third causes the error).

What you probably had in mind was to get three separate characters and concatenate them together, like "day[0]+day[1]+day[2]".