Change label text using JavaScript

Because your script runs BEFORE the label exists on the page (in the DOM). Either put the script after the label, or wait until the document has fully loaded (use an OnLoad function, such as the jQuery ready() or http://www.webreference.com/programming/javascript/onloads/)

This won't work:

<script>
  document.getElementById('lbltipAddedComment').innerHTML = 'your tip has been submitted!';
</script>
<label id="lbltipAddedComment">test</label>

This will work:

<label id="lbltipAddedComment">test</label>
<script>
  document.getElementById('lbltipAddedComment').innerHTML = 'your tip has been submitted!';
</script>

This example (jsfiddle link) maintains the order (script first, then label) and uses an onLoad:

<label id="lbltipAddedComment">test</label>
<script>
function addLoadEvent(func) {  
      var oldonload = window.onload;  
      if (typeof window.onload != 'function') {  
        window.onload = func;  
      } else {  
        window.onload = function() {  
          if (oldonload) {  
            oldonload();  
          }  
          func();  
        }  
      }  
    }  

   addLoadEvent(function() {  
document.getElementById('lbltipAddedComment').innerHTML = 'your tip has been submitted!';

    });  
</script>

Have you tried .innerText or .value instead of .innerHTML?

Because a label element is not loaded when a script is executed. Swap the label and script elements, and it will work:

<label id="lbltipAddedComment"></label>
<script>
    document.getElementById('lbltipAddedComment').innerHTML = 'Your tip has been submitted!';
</script>

Use .textContent instead.

I was struggling with changing the value of a label as well, until I tried this.

If this doesn't solve try inspecting the object to see what properties you can set by logging it to the console with console.dir as shown on this question: How can I log an HTML element as a JavaScript object?