I have the code as here in this jsfiddle, I want the font awesome icon to change on button click using javascript, but it does'nt seem to work. I'm new to javascript so please forgive me if this was a dumb question.

HTML

<button id="favBtn" onclick="fav();">
    <i id="favIcon" class="fa fa-star-o"></i>&nbsp;Favourite
</button>

Javascript

function fav() {
    document.getElementById("favIcon").toggleClass('fa-star-o fa-star');
}

When using jQuery you never need to use an inline attribute eventHandler.

`onclick=`

Demo 1 uses jQuery .toggleClass()
Demo 2 uses JavaScript .classList.toggle()
Demo 3 uses CSS :checked pseudo-class

Update v4 to v5: Go to Start | Font Awesome. There are some class changes as well. See Demo 4.

Demo 1 -- jQuery

$('button').on('click', fav);

function fav(e) {
  $(this).find('.fa').toggleClass('fa-star-o fa-star');
}

:root {
  font: 400 16px/1.5 Verdana;
}

button {
  display: inline-block;
  font: inherit;
  padding: 0px 5px;
  cursor: pointer;
}

button::after {
  content: ' Favorite'
}

<link href='https://cdn.jsdelivr.net/fontawesome/4.7.0/css/font-awesome.min.css' rel='stylesheet'>

<button>
    <i class="fa fa-star-o"></i>
</button>

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

Demo 2 -- Plain JavaScript

document.querySelector('button').addEventListener('click', fav);

function fav(e) {
  const tgt = e.target.firstElementChild;
  tgt.classList.toggle('fa-star');
  tgt.classList.toggle('fa-star-o');
}

:root {
  font: 400 16px/1.5 Verdana;
}

button {
  display: inline-block;
  font: inherit;
  padding: 0px 5px;
  cursor: pointer;
}

button::after {
  content: ' Favorite'
}

<link href='https://cdn.jsdelivr.net/fontawesome/4.7.0/css/font-awesome.min.css' rel='stylesheet'>

<button>
  <i class="fa fa-star-o"></i>
</button>

Demo 3 -- Pure CSS

:root {
  font: 400 16px/1.5 Verdana;
}

#fav {
  display: none
}

#fav+label {
  display: inline-block;
  border: 2px outset grey;
  padding: 0px 5px;
  cursor: pointer;
  -webkit-appearance: button;
  -moz-appearance: button;
  appearance: button;
}

#fav+label::after {
  content: ' Favorite'
}

#fav+label>.fa-star-o {
  display: inline-block
}

#fav+label>.fa-star {
  display: none;
}

#fav:checked+label>.fa-star-o {
  display: none;
}

#fav:checked+label>.fa-star {
  display: inline-block
}

<link href='https://cdn.jsdelivr.net/fontawesome/4.7.0/css/font-awesome.min.css' rel='stylesheet'>

<input id='fav' type='checkbox'>
<label for='fav'>
  <i class="fa fa-star-o"></i>
  <i class="fa fa-star"></i>
</label>

Demo 4 -- Font Awesome 5

jQuery / JavaScript / CSS

/* #1 jQuery */
$('button.jq').on('click', jQFav);
function jQFav(e) {
  $(this).find('.fa-star').toggleClass('fas far');
}

/* #2 JavaScript */
document.querySelector('button.js').addEventListener('click', JSFav);
function JSFav(e) {
  const tgt = e.target.firstElementChild;
  tgt.classList.toggle('far');
  tgt.classList.toggle('fas');
}

/* #1 JS / #2 jQ */
:root {
  font: 400 16px/1.5 Verdana;
}

button {
  display: inline-block;
  font: inherit;
  padding: 0px 5px;
  cursor: pointer;
}

button::after {
  content: ' Favorite'
}

/* #3 CSS */

#fav {
  display: none
}

#fav+label {
  display:inline-block;
  border: 2px outset grey;
  padding: 0px 5px;
  cursor: pointer;
  -webkit-appearance: button;
  -moz-appearance: button;
  appearance: button;
}

#fav+label::after {
  content: ' Favorite'
}

#fav+label>.far {
  display: inline-block;
}

#fav+label>.fas {
  display: none;
}

#fav:checked+label>.far {
  display: none;
}

#fav:checked+label>.fas {
  display: inline-block
}

<link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.8.2/css/all.css" crossorigin="anonymous">

<ol>
<li><fieldset>
<legend>jQuery</legend>

<button class='jq'>
  <i class='fa-star far'></i>
</button>

</fieldset></li>

<li><fieldset>
<legend>Plain JavaScript</legend>

<button class='js'>
  <i class='fa-star far'></i>
</button>

</fieldset></li>

<li><fieldset>
<legend>Pure CSS</legend>

<input id='fav' type='checkbox'>
<label for='fav'>
  <i class="fa-star far"></i>
  <i class="fa-star fas"></i>
</label>

</fieldset></li>
</ol>

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

Difster

.toggleClass() is a jQuery function and you're using it as JavaScript. Try this:

$("#favIcon").toggleClass('fa-star-o fa-star');

Difster's response is correct. Here is how you can accomplish the same thing using native JavaScript:

document.getElementById("favIcon").classList.toggle('fa-star-o');
document.getElementById("favIcon").classList.toggle('fa-star');

Additionally with what Difster said, .toggleClass is a jQuery function.

Beyond that, I wouldn't use the DOM to define bindings to functions; Using jQuery's event listener system will allow for more maintainable and understandable code:

https://jsfiddle.net/0n1n9o9n/2/

$(document).ready(function() {
  $('#favBtn').on('click', function() {
    $("#favIcon").toggleClass('fa-star-o fa-star');
  });
});

You can use only Javascript:

 function fav() {
    var icon = document.getElementById("favIcon");
      if (icon.classList.contains("fa-star-o")) {
        icon.classList.remove("fa-star-o");
        icon.classList.add("fa-star");
    } else {
       icon.classList.remove("fa-star");
       icon.classList.add("fa-star-o");
    }
 }

example

Redirod

I would split my comment into multiple remarks:

1/ As mentioned in the other comments: $("#favIcon").toggleClass('fa-star-o fa-star'); This is a mix of JS and JQuery calls. If you want to use pure JS you would use:

document.getElementById("favIcon").classList.toggle('fa-star-o');

If you want to use JQuery you can use () As mentioned in Difster's comment:

$("#favIcon").toggleClass('fa-star-o');

2/ As mentioned already in the comments, it's better to attach an event listener.

Your Fiddle js would look like this:

document.getElementById("favBtn").addEventListener("click", fav);
function fav() {
    document.getElementById("favIcon").classList.toggle('fa-star-o');
    document.getElementById("favIcon").classList.toggle('fa-star');
}

And remove the "onClick" on the HTML since you would be attaching a js event listener.

Links to check: JQuery toggleClass - js classList

Hope It Helps

$('.fa-star').click(function() {
  $(this).toggleClass('fas far');
})

 <link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.4.1/css/all.css" integrity="sha384-5sAR7xN1Nv6T6+dT2mhtzEpVJvfS3NScPQTrOxhwjIuvcA67KV2R5Jz6kr4abQsz" crossorigin="anonymous">


<script src="https://unpkg.com/jquery/dist/jquery.min.js"></script>

 
 
 
 
 
 <i class="far fa-star"></i>

来源：https://stackoverflow.com/questions/45245301/toggle-font-awesome-class-on-button-click

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javascript