javascript - 汇总一个数字，直到变成1位数JS(Sum up a number until it becomes 1 digit JS)

Question

Before you mark duplicate note that it isn't.(在标记重复注释之前，请注意不是。)

Others didn't look for the exact same thing as me.(其他人没有寻找和我完全一样的东西。)

What is the most compact possible way to sum up a number in javascript until there is only one digit left.(总结javascript中直到最剩下一位数字的最紧凑的方法是什么。)

For example: You input 5678 then the script adds it together (5+6+7+8) and gets 26, but since its more than 1 digit it adds it again and gets 2+6=8.(例如：您输入5678，然后脚本将其加在一起（5 + 6 + 7 + 8）并得到26，但是由于其大于1的数字，它将再次添加它并得到2 + 6 = 8。)

Is there anyway to do this with a number of any size?(无论如何，有任何大小的数字都可以做到这一点吗？)

And how compact can the script get?(脚本可以得到多紧凑？)   ask by Vincent translate from so

Answer 1

If you're looking for short, it's hard to beat:(如果您正在寻找短片，那就很难被击败：)

 var n = 5678; sum = n % 9 || 9; console.log(sum) 

If you're curious about how that works, see: casting out nines.(如果您对它的工作方式感到好奇，请参阅： 淘汰9。)