Binding multiple callbacks for promises returns resolve value of first promise, not second-CodePudding

I have the following code as part of some coding practice I am doing:

var promise = new Promise(function(resolve, reject) {
    setTimeout(function() {
        resolve('hello world');
    }, 2000);
});

var promiseTwo = new Promise((resolve, reject) => {
    setTimeout(() => {
        resolve('hello again!');
    }, 2000);
});

promise.then(promiseTwo).then((data) => {
    console.log(data)
})

When the data is logged, it reads hello world and not hello again!. Why is that? My thinking was that the line promise.then(promiseTwo).then((data) => { console.log(data) }) would resolve the first promise, then pass the second promise in as a callback which would resolve to hello again!. Why does the resolve in promiseTwo never get return from the .then method?

CodePudding user response：

Because you're not returning promiseTwo in then, you're simply calling it, try:

var promise = new Promise(function(resolve, reject) {
    setTimeout(function() {
        resolve('hello world');
    }, 2000);
});

var promiseTwo = new Promise((resolve, reject) => {
    setTimeout(() => {
        resolve('hello again!');
    }, 2000);
});

promise.then(() => promiseTwo).then((data) => {
    console.log(data)
})