The JS method parameter passed a number beginning with 0. A magical problem occurred and bothered me for a long time

Today I came across a magical problem , Make a special note of , It's very simple , Blame me for being too young ...

Here's the thing , One js Method to pass in a number , There is no problem at ordinary times , A simple example ：

//  Defined function 
function logNum(num) {
    
  console.log(num)
}

//  Call function 
logNum(123)

 Output results ：123

That's no problem, right ？

Today I passed in a special number ：0123, Something magical happened ：

How to become 83 了 ？？？

Does this figure have a special meaning ？ It can't be said like that ？

Try another number ：

It's hard to understand ！

later , Finally I found the same problem on the Internet ：

The answers are as follows ：

original 0 The first number is octal ！

Use octal calculator to calculate 0123 Converting to decimal is really 83 Well ！

Empathy , Hexadecimal numbers are in 0x At the beginning ：

I'm so young ！