I am a beginner and want to know how do I change the background colours of all the buttons on click?
var buttons = document.querySelectorAll(".btn").length;
for (var i = 0; i < buttons; i++) {
document.querySelectorAll(".btn")[i].addEventListener("click", function () {
document.querySelectorAll(".btn").style.backgroundColor = "red";
});
}<button class="btn">abc</button>
<button class="btn">abc</button>
<button class="btn">abc</button>
<button class="btn">abc</button>
<button class="btn">abc</button>
<button class="btn">abc</button>
<button class="btn">abc</button>
<button class="btn">abc</button>querySelectorAll returns a NodeList. You have to iterate through it and apply the style to each item:
var buttons = document.querySelectorAll(".btn").length;
for (var i = 0; i < buttons; i++) {
document.querySelectorAll(".btn")[i].addEventListener("click", function (e) {
document.querySelectorAll(".btn").forEach(e => e.style.backgroundColor = "red")
});
}<button class="btn">abc</button>
<button class="btn">abc</button>
<button class="btn">abc</button>
<button class="btn">abc</button>
<button class="btn">abc</button>
<button class="btn">abc</button>
<button class="btn">abc</button>
<button class="btn">abc</button>