Textarea Value Update Not Reflect In Page?

I'm trying to update a textarea's value with Javascript. The code is similar to:

console.warn("Before set, value is " + document.getElementById('myTextArea').value);
document.getElementById('myTextArea').value = 'OMGWTFBBQ';
console.warn("After set, value is " + document.getElementById('myTextArea').value);

Although the Firefox and Chrome consoles show that the value property is updated, this is not reflected in the page itself.The specific function is invoked from an onfocus handler of another element. The textarea itself is lazily initialised from the same method, by using:

var messageText = document.createElement('textarea');
messageText.id = 'myTextArea';
someParent.appendChild(messageText);

Obviously if I use the console rather than let the script run it does work.