In Javascript, all synchronous code in a given script is executed before any asynchronous code.

For example, take a look at the code below

setTimeout(() => {
  console.log("async");
}, 0);

for (let i = 0; i < 5; i++) {
  console.log("sync...", i);
}

The result of running the above block of code is

sync... 0
sync... 1
sync... 2
sync... 3
sync... 4
async

The delay on the setTimeout function is set to 0, but the handler function is executed last after all synchronous code has been executed.