how to pass resolved value

Question

what's wrong with this Promise using?

const count_elems = function(c){
  const elems = c.getElementsByTagName('p');
  console.log(elems.length);
};

const handler = function(){
    return new Promise(function (resolve, reject) {
     const cont = document.getElementById('cont');
     const p = document.createElement('p');
     for (let i=100000; i--;){
        cont.appendChild(p.cloneNode());
     }
     return resolve(cont);
  })
}

const test = function(){
  handler()
    .then(count_elems(c))
    .catch(function(e){console.log(e)});
};

document.getElementById('but')
  .addEventListener('click', test);

 <div id="cont"></div>
  <button id="but">click me</button>

There is no need for the promises, there is no asynchronous code anywhere. Are you expecting the promise to run on it's own thread? That is simply not the case though. Why JS uses promises is explained here: https://stackoverflow.com/a/47678417/1641941 — HMR, Dec 10 '17 at 07:00

Suren Srapyan · Accepted Answer · 2017-12-10T06:50:30.497

2

Get the c in the then function and then pass into the count_elems function. Also remove the return before the resolve, you don't need that.

.then(c => count_elems(c)) or just .then(count_elems) without function call.

const count_elems = function(c){
   const elems = c.getElementsByTagName('p');
   console.log(elems.length);
};

const handler = function() {

   return new Promise(function (resolve, reject) {
      const cont = document.getElementById('cont');
      const p = document.createElement('p');
      
      for (let i=100000; i--;){
         cont.appendChild(p.cloneNode());
      }
     
      resolve(cont);
  });
  
}

const test = function() {
   handler().then(c => count_elems(c))
            .catch(e => console.log(e));
};

document.getElementById('but')
        .addEventListener('click', test);

<div id="cont"></div>
<button id="but">click me</button>

edited Dec 10 '17 at 06:50

answered Dec 10 '17 at 06:24

Suren Srapyan

66,568
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114
112

code is works, but I expected that the container `cont` will be full... – shmnff Dec 10 '17 at 06:29
You mean `p` to be visible ? See the updated part. You need to create `p` in the for loop. – Suren Srapyan Dec 10 '17 at 06:30
not exactly visible but I mean that loop should finish before Promise resolving – shmnff Dec 10 '17 at 06:34
It is working like that. Loop is finished then Promise is resolved – Suren Srapyan Dec 10 '17 at 06:35
It is that IDE issue. If you will decrease the amount if the loop, you can see that it works correct. – Suren Srapyan Dec 10 '17 at 06:40
just checked in the browser, it seems that you are right – shmnff Dec 10 '17 at 06:46

score 1 · Answer 2 · answered Dec 10 '17 at 06:25

1

.then(count_elems(c)) should be .then(count_elems)

answered Dec 10 '17 at 06:25

Ultimater

4,647
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43

how to pass resolved value

2 Answers2