JSFiddle - React, Tailwind, and code Playground

HTML

<div id="hello">
    <div class="sub1">Hello how are you</div>
    <div class="sub2">Hello how are you</div>
    <div class="sub3">Hello how are you</div>
</div>
<input type="hidden" id="textbox" />

JavaScript

var arr = ['a', 'a', 'b', 'a', 'c'];

var indexA = [];
for (var i = 0; i < arr.length; i++) {

    if ("a" == arr[i]) indexA.push(i)
}
alert(indexA);