如何在JavaScript中交替使用2个循环？

Question

I have two loops. How can I run them alternately? For example output of this code:

for (var i = 15; i >= 10; i--) {
  console.log(i)      
}
for (var t = 15; t <= 20; t++) {
  console.log(t)
}

will be:

15 // first loop started
14
13
12
11
10 // first loop ended
15 // second loop started
16
17
18
19
20 // second loop ended

What should i do to get this output:

15 //first loop started
15 //second loop started
14 //first 
16 //second
13 //first
17 //second
12 //first
18 //second
11 //first
19 //second
10 //first loop ended
20 //second loop ended

Answer 1

You could put both initialization , condition and final-expression parts in one for loop.

 for (var i = 15, t = 15; i >= 10 && t <= 20; i--, t++) { console.log(i) console.log(t) }