How to switch pictures by pressing the button?

Question

I am learning how to create websites. I want to build a simple theme switcher with HTML/CSS/JavaScript. I've done the theme switching part, but I want to change the picture in the button when I press it.

Here is my moon picture: (https://www.svgrepo.com/svg/6390/moon) and here is my sun picture: (https://www.svgrepo.com/svg/304624/sun-light-theme).

Here is my code:

const btn = document.querySelector('.btn_theme');
btn.addEventListener('click', function() {
  document.body.classList.toggle('dark_theme');
});

body {
  background-color: white;
  color: black;
  font-family: "Trebuchet MS", Helvetica, sans-serif;
  font-size: 16pt;
  font-weight: normal;
}

body.dark_theme {
  background-color: #2F3136;
  color: white;
  font-size: 16pt;
  font-weight: normal;
  font-family: "Trebuchet MS", Helvetica, sans-serif;
}

.container {
  width: 100px;
  height: 55px;
  background-color: #2F3136;
  color: white;
  text-align: center;
  border-radius: 10px;
  position: absolute;
  display: flex;
  align-items: center;
}

.btn_theme {
  text-align: center;
  width: 90px;
  height: 45px;
  background-color: white;
  margin: 0;
  padding: 0;
  border: 0;
  left: 5px;
  border-radius: 8px;
  position: relative;
  transition: all .15s linear;
  -webkit-transition: all .15s linear;
  -moz-transition: all .15s linear;
  align-items: center;
}

button:hover {
  background-color: #2f3647;
  transition: all 0.15s linear;
  -webkit-transition: all 0.15s linear;
  -moz-transition: all 0.15s linear;
}

<p>text</p>
<div class="container">
  <button class="btn_theme" id="btn_theme"><img src="../imgs/солнце.svg" /></button>
</div>

Answer 1

You need to update the src attribute of your image using setAttribute().

You could use modular arithmetic to switch between pictures. This would work for however many pictures you want to have. It is however not required for a two images as you could just use a boolean. Nevertheless here how you could do it using modulo operation.

// All the pictures we want to switch between
const pics = [
  "https://dummyimage.com/50x50/000/fff",
  "https://dummyimage.com/50x50/dddddd/000",
  // "https://dummyimage.com/50x50/d420d4/000" // comment this out for a third pic
]
let curPicIdx = 0;

window.addEventListener("DOMContentLoaded", e => {
  // when the page has loaded set the first picture
  const button = document.getElementById("mybutton");
  const img = document.getElementById("myimage");
  img.setAttribute("src", pics[curPicIdx])
  
  // whenever we click on the button change the picture to the next one
  button.addEventListener("click", e => {
    // calculate the index of the next picture using modular arithmetic
    curPicIdx = (curPicIdx + 1) % pics.length;
    console.log(`Setting pic ${curPicIdx}`);
    // set the next picture using the calculated index
    img.setAttribute("src", pics[curPicIdx]);
  })
})

<button id="mybutton"><img id="myimage"/>

If you want to have three pictures, just add another URL within the array and it will switch between all three pictures.

In general there are a lot of ways to embed images into buttons. You might wanna have a look at this thread.

Answer 2

There are a couple ways to accomplish this.

One way is to just get rid of the img tag and change the button's background image.

const btn = document.querySelector('.btn_theme');
btn.addEventListener('click', function() {
  document.body.classList.toggle('dark_theme');
});

.btn_theme {
  background: url('https://www.svgrepo.com/show/304624/sun-light-theme.svg');
  text-align: center;
  width: 40px;
  height: 40px;
  background-color: white;
  margin: 0;
  padding: 0;
  border: 0;
  left: 5px;
  border-radius: 8px;
  position: relative;
  transition: all .15s linear;
  -webkit-transition: all .15s linear;
  -moz-transition: all .15s linear;
  align-items: center;
}

button:hover {
  background-color: #2f3647;
  transition: all 0.15s linear;
  -webkit-transition: all 0.15s linear;
  -moz-transition: all 0.15s linear;
}

.dark_theme {
  background: #ffaaff
}

.dark_theme .btn_theme {
  background: url('https://www.svgrepo.com/show/6390/moon.svg');
}

<button class="btn_theme" id="btn_theme"></button>

Another solution is to use a data-attribute to store the current state and change the img tag's src value.

const btn = document.querySelector('.btn_theme');
const icon = btn.querySelector('img');
btn.addEventListener('click', function() {
  document.body.classList.toggle('dark_theme');

  if (icon.dataset.theme == "light") {
    icon.dataset.theme = "dark";
    icon.src = "https://www.svgrepo.com/show/6390/moon.svg";
  } else {
    icon.dataset.theme = "light";
    icon.src = "https://www.svgrepo.com/show/304624/sun-light-theme.svg";
  }


});

.btn_theme {
  text-align: center;
  width: 40px;
  height: 40px;
  background-color: white;
  margin: 0;
  padding: 0;
  border: 0;
  left: 5px;
  border-radius: 8px;
  position: relative;
  transition: all .15s linear;
  -webkit-transition: all .15s linear;
  -moz-transition: all .15s linear;
  align-items: center;
}

button:hover {
  background-color: #2f3647;
  transition: all 0.15s linear;
  -webkit-transition: all 0.15s linear;
  -moz-transition: all 0.15s linear;
}

.dark_theme {
  background: #ffaaff
}

<button class="btn_theme" id="btn_theme"><img class="icon" data-theme="light" src="https://www.svgrepo.com/show/304624/sun-light-theme.svg"></button>