input.onSetFocus = function(old:TextField):Void  {
			 Selection.setSelection(0, 0);
			 var lo:Object = new Object();
			 lo.tf = this;
			lo.onMouseUp = function() {
				trace(this.tf);
				Selection.setSelection(0, this.tf.text.length);
				Mouse.removeListener(this);
			};
				Mouse.addListener(lo);
		 };

Make text field content selected and drop selection from the text field selected before. For AS2

ActionScript