Execute javascript function after previous one finishes

Question

I have the function "showElement" that has a setTimeout. How can I make that the calls to the function in the eventListener of the 'btnSend' execute one right after the other one?

I tried with .then() but didn't work.

document.getElementById('btnSend').addEventListener('click', e => {
    e.preventDefault();
    result = validateInputs(email, subject, message);
    if(result) {
        showElement(document.getElementById('formGroupSpinner'), 2000);
        showElement(document.getElementById('formGroupSuccessImg'), 2000);
        resetForm();
    }
});

//expects an html element and a number representing miliseconds. Shows the html element for that amount of time.
function showElement(element, mSeconds) {
    element.classList.remove('d-none');
    element.classList.add('d-block');
    setTimeout( () => {
        element.classList.remove('d-block');
        element.classList.add('d-none');
    }, mSeconds);
}

Both functions execute at the same time.

Answer 1

There's many different approaches to this but I would suggest using a Promise like this:

 document.getElementById('btnSend').addEventListener('click', e => { e.preventDefault(); var result = validateInputs(email, subject, message); if(result){ showElement(document.getElementById('formGroupSpinner'), 2000).then(()=>{ return showElement(document.getElementById('formGroupSuccessImg'), 2000); }).then(()=>{ resetForm(); }); } }); //expects an html element and a number representing miliseconds. Shows the html element for that amount of time. function showElement(element, mSeconds) { return new Promise((resolve, reject) => { element.classList.remove('d-none'); element.classList.add('d-block'); setTimeout( () => { element.classList.remove('d-block'); element.classList.add('d-none'); resolve(); }, mSeconds); }); } 

Basically, the function after the .then() only gets executed once you called the resolve(); .

Alternatively you could also use a callback or async / await .

Answer 2

you could use a callback to execute other instructions after the function has ended:

//First you add a param "callback" to the function
function showElement(element, mSeconds, callback) {
    element.classList.remove('d-none');
    element.classList.add('d-block');
    setTimeout( () => {
        element.classList.remove('d-block');
        element.classList.add('d-none');
        //Then you ask if the callback function is present and call it
        if(callback && typeof callback === "function") callback();
    }, mSeconds);
}

//Then use it in your event like this:
document.getElementById('btnSend').addEventListener('click', e => {
    e.preventDefault();
    result = validateInputs(email, subject, message);
    if(result) {
        showElement(document.getElementById('formGroupSpinner'), 2000, () => {
            showElement(document.getElementById('formGroupSuccessImg'), 2000);
            resetForm();
        });  
    }
}); 

Answer 3

You can do this by using Promise . You have to wrap your showElement() function into a promise and call the promise resolver once setTimeout fires. Then your calling code can pipe your the promises together with then :

showElement(document.getElementById('formGroupSpinner'), 2000).then(() => {
    showElement(document.getElementById('formGroupSuccessImg'), 2000).then(() => {
        resetForm();
    });
});

However, this quickly leads to callback hell.

You can avoid this by using async/await . You mark your function as async , then you can use await within it to wait for the promises to resolve before continuing to the next one:

await showElement(document.getElementById('formGroupSpinner'), 2000);
await showElement(document.getElementById('formGroupSuccessImg'), 2000);
resetForm();

Here is a working demo:

 document.getElementById('btnSend').addEventListener('click', async e => { e.preventDefault(); await showElement(document.getElementById('formGroupSpinner'), 2000); await showElement(document.getElementById('formGroupSuccessImg'), 2000); }); function showElement(element, mSeconds) { return new Promise((resolve, reject) => { element.classList.remove('d-none'); element.classList.add('d-block'); setTimeout(() => { element.classList.remove('d-block'); element.classList.add('d-none'); resolve(); }, mSeconds); }); } 

 .d-none { display: none; } .d-block { display: block; } 

 <button id="btnSend">Send</button> <div id="formGroupSpinner" class="d-none">Spinner</div> <div id="formGroupSuccessImg" class="d-none">Success image</div> 

Answer 4

The simplest way to do what you want is simply changing the second showElement to 4000 instead of 2000 .

That way one will have a timeout of 2 seconds and the other 4 seconds.

Answer 5

To make a promise chain, you first have to have a promise.

function showElement(element, mSeconds) {
  return new Promise(function(resolve,reject){
    element.classList.remove('d-none');
    element.classList.add('d-block');
    setTimeout( () => {
      element.classList.remove('d-block');
      element.classList.add('d-none');
      resolve();
    }, mSeconds);
  }
}

Then you can use showElement().then(/*something here */)