动态确定for循环的顺序

Question

I need to be able to dynamically read an array from either the start or the end, and work up or down from that position.

This is decided by a boolean: var startFromBeginOfChat = true;

I tried to pass a statement inside the for loop, like so:

for (var i = startFromBeginOfChat ? (parsedChat.messages.length - 1):0; 
startFromBeginOfChat ? (i >= 0):(i < parsedChat.messages.length); 
startFromBeginOfChat ? i--:i++) 

Is there any other way to dynamically fire either one or another for loop? I could of course store the entire logic into an if/else statement but since the logic inside the for loop is exactly the same, I'd rather not.

Answer 1

As stated in the comments, you can just reverse the list beforehand if you need to parse it backwards. The entire final code would be the following:

if (!startFromBeginOfChat) parsedChat.messages.reverse();

for (var i = 0; i < parsedChat.messages.length; i++) {
   // code
}

If you need the original list to be in order again, you could either reverse it again at the end (potentially more efficient, but less semantic) or create a new copy before you originally reverse it by using parsedChat.messages.slice() (more readable in my opinion).