JSFiddle - React, Tailwind, and code Playground

HTML

<body>
  <div id="greeting"></div>
  <p id="prompt1">Fill up sides A, B, then C, angles in degrees <strong>(Warning: does not test for amibiguous case)</strong></p>
  <form id="form1" action="form_action.asp">
    Side A:  <input type="Number" name="sideA"><br>
    Side B:  <input type="Number" name="sideC"><br>
    Side C:  <input type="Number" name="sideC"><br>
    Angle A:  <input type="Number" name="angleA"><br>
    Angle B:  <input type="Number" name="angleB"><br>
    Angle C:  <input type="Number" name="angleC"><br>
    <input type="button" onclick="init()" value="Submit"/>
  </form>
  <p id='test'></p>

</body>

JavaScript

function degToRad(num) {
  if (num === undefined) { return; }
  return Math.PI * num / 180;
}


function init() {
 
  var text = document.querySelector("#form1");
  sideA = text.elements[0].value;
  sideB = text.elements[1].value;
  sideC = text.elements[2].value;
  angleA = degToRad(text.elements[3].value);
  angleB = degToRad(text.elements[4].value);
  angleC = degToRad(text.elements[5].value);
  whatWeGot();
}

//determine which algorithm to go to and run it
function whatWeGot() {
  if (!(angleA >0 && angleB >0 && angleC >0)) {
    algSSS();
  } else if (sideC === undefined && angleB === undefined && angleC === undefined) {
    algSSA();
  } else if (sideB === undefined && sideC === undefined) {
    if (angleC === undefined) { angleC = Math.PI - (angleA + angleB); }
    else if (angleB === undefined) { angleB = Math.PI - (angleA + angleB); }
    else { angleA = Math.PI - (angleB + angleC); }
    algASA();
  }
}

function algSSS() {
     document.getElementById('test').innerHTML = 'sss worked';
}