how to pass input field value in javascript function code example

Example 1: passing html vlaues to Javascript function

<body>
<h1>Adding 'a' and 'b'</h1>

  a: <input type="number" name="a" id="a"><br>
  b: <input type="number" name="b" id="b"><br>
  <button onclick="add(document.getElementById('a').value,document.getElementById('b').value)">Add</button>

<script>
  function add(a,b) {
    var sum = parseInt(a) + parseInt(b);
    alert(sum);
  }
</script>
</body>

Example 2: javascript function with input value

<button class="btn btn-primary" onclick="transmit({search: document.getElementById('search_id').value});">
	<span class="glyphicon glyphicon-search"></span>
</button>