HTML

No selection

oncontextmenu="return false;" onselectstart="return false"

add this in tag, broswer will not allow user to select this element. It’s helpful to set a button, because sometimes user will select the text on the button, and it will affect experience.

Javascript

Circle index in Array

When design a photo album, developer usually collect all src (link) of image in a Array, and control index to choose a link then exhibit on HTML.

When user click button, the index will increase or decrease, and the img tag will update src. But the array has a fixed length, if index bigger / less than length / 0, it will be a problem.

So I found this code:

while (index < 0) index += srcArr.length
while (index > srcArr.length) index -= srcArr.length

It means, if the index become negative, it will become the last element in array, as well as other situation (first). So index will circle change.