JS hoisting: how to break the chain of Promise calls

How to break the chain of Promise calls?

Problem: When the state of promise changes, his chained calls will take effect, then if we have this actual requirement: we have 5 then(), but there are conditional judgments, such as when I meet or not meet the firstWhen there are three then conditions, how to directly interrupt the chain call and no longer go to the following then?

We know that Promise has three states: pending (in progress), fulfilled (successful) and rejected (failed), when the state changes from pending (in progress)) becomes fulfilled (successful) or rejected (failed), the then method of Promise will be called. If it has been in the pending (in progress) state, the then method will not be executed.

Then we can use this to interrupt the chained call of Promise, and return a Promise object in the pending (in progress) state in the callback function, so that the then method will notimplemented.

The principle here is that the result state of the new promise returned by promise.then() is determined by the result of the callback function specified by then().That is:

If an exception is thrown, the new promise becomes rejected, and the reason is the thrown exception
If any value other than a promise is returned, the new promise becomes resolved, and value is the returned value
IfWhat is returned is another new promise, and the result of this promise will become the result of the new promise
So we return a promise object in the pending (in progress) state in promise.then(), The result status of the new promise returned by promise.then() is always pending (in progress), and the then method will not be executed.

let p = new Promise((resolve, reject) => {setTimeout(() => { resolve('OK');}, 1000);});p.then(value => {return new Promise(() => {});}).then(value => { console.log(222);}).then(value => { console.log(333);}).catch(reason => {console.warn(reason);});

Never decide

new Promise(resolve=>{resolve(1);}).then(value=>{console.log(value)return 2}).then(value=>{console.log(2)return new Promise(()=>{})}).then(value=>{console.log(value);return 4;}).then(value=>{console.log(value);return 5}).catch(error=>{console.log(error,'===');})

Original link: https://blog.csdn.net/cckevincyh/article/details/124796139