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Hanwen Zhang
20,084 PointsQuestion : if (prevLi) {ul.insertBefore(li, prevLi);} and if (nextLi) {ul.insertBefore(nextLi, li)} .
What do the preLi and nextLi works in the if argument "if (prevLi) & if (nextLi) " here?
if (event.target.className == 'up') {
let li = event.target.parentNode;
let prevLi = li.previousElementSibling;
let ul = li.parentNode;
if (prevLi) {
ul.insertBefore(li, prevLi);
}
}
if (event.target.className == 'down') {
let li = event.target.parentNode;
let nextLi = li.nextElementSibling;
let ul = li.parentNode;
if (nextLi) {
ul.insertBefore(nextLi, li);
}
1 Answer
Peter Vann
36,425 PointsHi Hanwen!
I hope I am understanding your question.
Basically if (prevLi) and if (nextLi) is logic that, in effect, says only perform the related insertBefore if that (previous or next, respectively) list item exists, and if it doesn't, do nothing.
By the way, this kind of logic is what they call "truthy" and "falsy".
Essentially if the value exists, it logically is "truthy" (meaning will not resolve to false).
If it does not exist (null), then it logically is "falsy" (meaning will not resolve to true).
More info:
https://www.sitepoint.com/javascript-truthy-falsy/ (a pretty thorough explanation).
Does that answer your question?
I hope that helps.
Stay safe and happy coding!
Hanwen Zhang
20,084 PointsHanwen Zhang
20,084 PointsHi Peter,
You definitely did answer my question. Thank you so much!!!