I’m practicing my vanilla JS and trying to create dynamic elements. I came across some interesting behavior. I am simply creating a button, click it and then have it render onto the DOM. But then I want to create another event that mouses over the h1 elements and changes the color, however I get a “Uncaught TypeError: Cannot read property ‘addEventListener’ of null”. Why is this showing up as null if there is a h1 on the DOM and why does it now say cannot read property “addEventListener” of null?
HTML <!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta http-equiv="X-UA-Compatible" content="IE=edge"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <title>Creating Dynamic Elements</title> </head> <body> </body> </html>
JavaScript
// const h1 = document.querySelectorAll('h1');
const button = document.createElement('button');
button.textContent = "Click me";
document.querySelector('body').appendChild(button);
button.addEventListener('click', function() {
const h1 = document.createElement('h1');
h1.textContent = 'Hello World!';
document.querySelector('body').appendChild(h1);
});
document.querySelector('h1').addEventListener('mouseover', function() {
alert("It works!");
});
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Answer
Add your h1 event listener inside the function since there’s no h1 on load.
const button = document.createElement('button');
button.textContent = "Click me";
document.querySelector('body').appendChild(button);
button.addEventListener('click', function() {
const h1 = document.createElement('h1');
h1.textContent = 'Hello World!';
document.querySelector('body').appendChild(h1);
h1.addEventListener('mouseover', function() {
alert("It works!");
});
});