how to set fous on webform controls

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C#

Javascript

I want to set focus on control i clicked but my code not working
Here is my code

else if (answer is HandwrittenAnswer)
{
  this.Sourcecode.AppendLine("\t\t\t\t<textarea id='" + id + "' name='" + id + "' value='' style='position: absolute; "
                                                         + "top: " + top + "px; left: " + left + "px; height: " + height + "px; width: " + width + "px; "
                                                         + "visibility: hidden; z-index: 2; resize: none;'></textarea>");
  this.Sourcecode.AppendLine("\t\t\t\tdocument.getElementById id='" + id+ "' .focus();");
}

with above code when i click on my web form it goes inside the control i click but there is no focus set it means when i click text box is opened and when i write something nothing happens because there is no focus so i need to click one more time then can write something but i want to set focus directly when i click on my control.
Anyone got idear whats wrong ?????Solution