javascript中如何使函数同步执行？ 或者如何让函数一个接一个地执行？

Question

Here is my function

function two(){
    console.log('two')

}

function one(callback){
    setTimeout(()=>{
        console.log('one')        
    },2000)
    callback()
}

one(two)

Actual output:

two  
one  

My expected Output:

one  
two  

My question is how to make changes to these functions so that function two() will be executed after function one()

Answer 1

You could simply call the callback() in your setTimeout 's anonymous function like so:

 function two() { console.log('two') } function one(callback) { setTimeout(() => { console.log('one'); callback(); // execute callback after everything in setTimeout is executed }, 2000); } one(two);

... or, instead, you can use a Promise with ES7's async/await (or using a .then() callback) capabilities like so:

 function two() { console.log('two') } async function one(callback) { // make async so we can use `await` await new Promise((resolve, rej) => { // wait for the promise to resolve... setTimeout(() => { console.log('one'); resolve(); }, 2000) }); callback(); //... then execute the callback } one(two);

Answer 2

This works

let one = new Promise((resolve, reject) =>{
  setTimeout(()=>{
      console.log('one')
      resolve(true)
  },2000)
})


one.then((value) => {
    console.log('two')
})

Answer 3

I think callback will be called before other execution.This also works.

    function two(){
        console.log('two')
    }

    function one(one, callback){
        console.log(one);
        callback()
    }

    one('one', two);