Synchronous task (macro task, micro task), asynchronous task

First look at the results of the following code

console.log(1)
process.nextTick(function(){
    console.log(2)
})
setTimeout(function(){
    console.log(3)
    process.nextTick(function(){
        console.log(4)
    })
})
Promise.resolve().then(function() {
    console.log(5);
}).then(function() {
    console.log(6)
});Copy the code

The priorities of synchronization tasks, micro tasks, and macro tasks are as follows:

Synchronization Task > Micro Task > Macro TaskCopy the code

Macro tasks include

# The browser Node
I/O ✅ ✅
setTimeout ✅ ✅
setInterval ✅ ✅
setImmediate ❌ ✅
requestAnimationFrame ✅ ❌

Microtasks include

# The browser Node
process.nextTick ❌ ✅
MutationObserver ✅ ❌
Promise.then catch finally ✅ ✅

Back to the problem

1. The first line is the synchronization task, which has the highest priority, so the first output is 1.setTimeout is a macro task, sosetNextTick prints 2, 4, followed by another microtask. Promise prints 5,6, 5, followed by the macro tasksetTimeout, print 3setThere is a microtask in Timeout, and then execute it, printing 4Copy the code

// So it's 1, 2, 5, 6, 3, 4Copy the code