This function interacts with HTML elements to convert a number from one unit of measurement to another.

convertUnit.js

function convertUnit() {
  //check to see if the input is a number

  var input = document.getElementById("userInput").value
  var startUnit = document.getElementsByName("startUnit");
  var endUnit = document.getElementsByName("endUnit");
  var output = ""

  //check to see if input is a number
  if (isNaN(input) == true) {
    alert("Please input a valid number");

  }

  //check to make sure all of the radio buttons are checked
  if (startUnit[0].checked == false && startUnit[1].checked == false) {
    alert("Please select the unit you are converting from");
  }
  if (endUnit[0].checked == false && endUnit[1].checked == false) {
    alert("Please select the unit you are converting to");
  }
  
  //check to see if the start unit is grams
  if (startUnit[0].checked == true) {
    console.log("start at grams");
    //check to see if the end unit is grams
    if (endUnit[0].checked == true) {
      //convert grams to grams - take no action
      output = (input + " grams = " + input + " grams ")
      console.log("end at grams");
    }
    //check to see if the end unit is pounds
    if (endUnit[1].checked == true) {
      //convert grams to pounds - multiply input by 0.00220462262185
      var conversion = input * 0.00220462262185
      output = (input + " grams = " + conversion + " lb ")
      console.log('end at pounds');
    }
  }
  //check to see if the start unit is pounds
  if (startUnit[1].checked == true) {
    console.log("start at pounds");
    //check to see if the end unit is pounds
    if(endUnit[1].checked == true) {
      //convert pounds to pounds - take no action
      output = (input + " pounds = " + input + " pounds")
      console.log("end at pounds")
    }
    //check to see if end unit is grams
    if(endUnit[0].checked == true) {
      //convert pounds to grams
      conversion = input / 0.00220462262185
      output = input + " pounds = " + conversion + " grams"
    }
  }
  document.getElementById("output").innerHTML = output
}