How to add if input is empty within this code? Javascript, not jQuery.

currently a beginner learning javascript but I'm a bit stuck on how to add in this code if the inputs are empty, to shoot an alert. Would I add another function within the first? Any hints would be appreciated!

function getCandidateNames() {
var inputs = document.getElementsByTagName("input");
var result = [ ];
  for ( var i = 0; i < inputs.length ; i += 1) {
    if ( inputs[i].getElementsByTagName("candidate") ) {
      result.push( inputs[i].value );
    }
}
    return result;
}

function putCandidateNames(names) {
 document.getElementById("candidateName1").innerHTML = names[0];
 document.getElementById("candidateName2").innerHTML = names[1];
 document.getElementById("candidateName3").innerHTML = names[2];
}

function candidateNames() {
  putCandidateNames ( getCandidateNames() ) ;
}

The HTML

<fieldset id="candidates">
        <legend>Candidates</legend>
        <div>
            <label for="cand1">Candidate 1</label>
            <input class="candidate" id="cand1" placeholder="Candidate">
        </div>
        <div>
            <label for="cand2">Candidate 2</label>
            <input class="candidate" id="candName" placeholder="Candidate">
        </div>
        <div>
            <label for="cand3">Candidate 3</label>
            <input class="candidate" id="candName" placeholder="Candidate">
        </div>
    </fieldset>