Java select entire value in form field

How do I select the entire value in the field in addition to setting focus as I have below.

        function DynamCkTextBox(thisTextBox) {
            var dVal = 0;

            if (isNaN(thisTextBox.value)) {
                thisTextBox.focus();
                alert('"' + thisTextBox.value + '" is not a valid value for field ' + thisTextBox.id);
                //thisTextBox.style.backgroundColor = "Yellow"
                return false;
            }
            //thisTextBox.style.backgroundColor = "White"
            dVal = Number(thisTextBox.value);
            thisTextBox.value = dVal.toFixed(2);
            return true;
        }