Node.js setTimeout, setImmediate how do they work?

Question

JavaScript

When this code is called, the functions are called in a different order, please explain why?!
function a() {console.log(1);}
function b() {console.log(2);}
setTimeout(a, 0);
setImmediate(b, 0);
-------------------------------------
In this code, always strictly a, then b. Why not in the first case?
function a() {console.log(1);}
function b() {console.log(2);}
setTimeout(a, 0);
setTimeout(b, 0);

Answer 1

The delay in setTimeout can be from 1 to 2147483647 ms. All other values ​​are referenced to 1 ms !