我想弄清楚这里出了什么问题

Question

I am writing some code and I keep getting the error of "document.getElementsByClassName". Here is my code. What could be wrong?`

$("#pre-order").change(function(){   updateDisplay();})
function updateDisplay(){
 var preo = document.getElementsByClassName('product-single__meta');
 preo.addClass('preorder');
 }
 updateDisplay();

Answer 1

Why are you combining jquery with regular javascript. you could do

var preo = $('.product-single__meta');

or even better. one liner

$('.product-single__meta').addClass('preOrder');

Answer 2

That does add the class but when the id of pre-order is not present I don't need the preorder class.