how to have text appear inside a text input code example

Example: how to get the input of a textbox in html

//HTML Textbox w/Getting Javascript Input:
<script>
  function getTextBox(){
    var k = document.getElemntById('myTextBox').value
    alert(k)
  }
</script>
<input type="text" id="myTextBox">
<button onclick="getTextBox()">Get Text Input</button>