JSFiddle - React, Tailwind, and code Playground

HTML

<body>

<form id = 'table' name = 'table'>
<p> Gimme a number </p>
<input id = 'textbox' type = 'number' name = 'inputBox'>
<input id = 'button' type = 'button' value = 'Submit' onclick = 'check()'>

</form>
</body>

JavaScript

function check(){
	var number = document.table.inputBox.value;
var array = [number];
array.push(number+number);
alert(array);
}