Welcome to the Treehouse Community
The Treehouse Community is a meeting place for developers, designers, and programmers of all backgrounds and skill levels to get support. Collaborate here on code errors or bugs that you need feedback on, or asking for an extra set of eyes on your latest project. Join thousands of Treehouse students and alumni in the community today. (Note: Only Treehouse students can comment or ask questions, but non-students are welcome to browse our conversations.)
Looking to learn something new?
Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and a supportive community. Start your free trial today.
Peter Huang
5,426 PointsDifference between " for in " and " for loop "
what is the Difference between " for in " and " for loop "
Somehow they look the same but upon my research, some is saying to not use for in for arrays?
1 Answer
Steven Parker
220,683 PointsPerhaps the main difference is that a standard "for" loop will return the index as a number, but a "for in" will return it as a string. This is the primary reason that the standard "for" is recommended when iterating arrays.
Peter Huang
5,426 PointsThank you Steven. From your experience, how often do you do you see people use " for in " in real projects? I understand " for " very well and plan to stick by it. Wondering if " for in " is something I should be too concerned about and tackle that or not.
Steven Parker
220,683 PointsThe "for in" loop is used all the time with objects in real projects, but typically not with arrays. Now another loop type that is used with arrays is "for of".
Trent Stenoien
Full Stack JavaScript Techdegree Graduate 20,034 PointsTrent Stenoien
Full Stack JavaScript Techdegree Graduate 20,034 PointsThey serve a similar purpose, but a 'for' loop are for arrays while 'for...in' loops are for objects. In the 'for' loop below, you see we set i = 0, then increment by one while i < array.length. We can then call 'array[i]' as we go along. Technically, arrays are objects in JS though so 'for...in' loops work on arrays too. I don't know the performance differences, but I like how many more options there are in 'for' loops so that's what I tend to use.
for (let i = 0; i < array.length; i++) { ... } for (const property in object) { ... }