CODEWITHSUNDEEP
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Reputation: 457

Call Promise when setTimeout function is complete

I'm trying to implement Promise statements in my code and would love some help. I have a function that runs with a setTimeout. I want to call a function once that is completed.

Tried including Promise statements, but I have a feeling I'm not doing it correctly. Any feedback is helpful

function App(){

        let exampleProm = new Promise(
            function(){
                    type.type("hello , dexter", 100);
            }
        ).then(console.log('finished'));

}

App();

//code that gets called first

module.exports = {
    type: function(phrase, delaySpeed){
        let total = 0;
        let empty = [];
        for(let i = 0; i < phrase.length;i++){
            total += delaySpeed;
            setTimeout(() => {
                empty.push(phrase.charAt(i));
                process.stdout.write(chalk.blue.bold(empty[i]));
                if(empty.length === phrase.length){ //if complete
                    process.stdout.write('\n'); //puts on separate line
                }
            },total);
        }
    }
}

Upvotes: 0

Views: 87

Answers (2)

charlietfl
charlietfl

Reputation: 171700

Use an array of promises that each resolve() inside the setTimeout() and then Promise.all() to run the code after they have all resolved

module.exports = {
  type: function(phrase, delaySpeed) {
    let total = 0;
    let empty = [];
    let promises = []
    for (let i = 0; i < phrase.length; i++) {
      total += delaySpeed;
      // new promise for each character
      let promise = new Promise(function(resolve, reject) {
        setTimeout(() => {
          empty.push(phrase.charAt(i));
          process.stdout.write(chalk.blue.bold(empty[i]));
          if (empty.length === phrase.length) { //if complete
            process.stdout.write('\n'); //puts on separate line
          }          
          // assuming above writes are synchronous can now resolve promise
          resolve()
        }, total);

      });
      // push new promise to array
      promises.push(promise)
    }
    // return the all() promise
    return Promise.all(promises)// add another then() if you need to return something to next then() in App()
  }
}

function App(){    
     type.type("hello , dexter", 100).then(function(){
         // this then() fires when the Promise.all() resolves
         console.log('finished')
     });    
}

Upvotes: 2

Dan Balaban
Dan Balaban

Reputation: 735

The reason your .then handler never gets called is because the promise is stuck in its initial state, which is "pending".

Promises can be pending or settled (fulfilled / rejected). The callback passed to a Promise constructor takes two params, resolve (trigger a fulfill) and reject (trigger a rejection).

var promise1 = new Promise(function(resolve, reject) {
  setTimeout(function() {
    resolve('foo');
  }, 300);
});

promise1.then(function(value) {
  console.log(value);
  // expected output: "foo"
});

Check out the source for the code above at the MDN docs for the Promise API.

I reckon the example above gives you a hint on how to implement promise based delays, but if you need further assistance, let me know.

Upvotes: 1

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