JSFiddle - React, Tailwind, and code Playground
HTML
<span class="myclass">123</span>
<span class="myclass">456</span>
<span class="myclass">789</span>JavaScript
var arr = [];
var matches = document.querySelectorAll("span.myclass");
for(var i = 0; i < matches.length; i++){
arr[i] = parseInt(matches[i].innerHTML, 10);
}
console.log(arr);// [123, 456, 789]