JSFiddle - React, Tailwind, and code Playground

HTML

<form id="form1">
    
    <input class="input1" type="text">
    
</form>

JavaScript

/*
function auto_insert(formID,fieldClass,value) {
    var $formID = document.getElementById(formID);
    $($formID).find("."+fieldClass).val(value);
    
}
auto_insert("form1","input1","foo");
*/


function auto_insert(formID,fieldClass,value) {
    var $formID = document.getElementById(formID);
    var inputEls = $formID.getElementsByTagName("input");
    for(i = 0; i < inputEls.length; i++){
        if (inputEls[i].className == fieldClass) {
            inputEls[i].value = value;
            }
    }
    
}
auto_insert("form1","input1","foo");