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
Peter Huang
5,427 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
231,261 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
5,427 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
231,261 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 21,632 PointsTrent Stenoien
Full Stack JavaScript Techdegree Graduate 21,632 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) { ... }