TextArea_javascript 기술에서 텍스트를 선택하는 JS 방법

<script type="text/javascript">
  function select_field(id){
    document.getElementById(id).focus();
    document.getElementById(id).select();
  }
  function init(){
    select_field('text1');
  }
  onload=init;
</script>
<form>
This field gets selected onload:<br/>
<input type="text" name="text1" id="text1" value="some text" />
<br/>
<textarea name="textarea1" id="textarea1" rows="9" cols="50" wrap="off">Some long
content in here.
abcd efgh abcd efgh abcd efgh
abcd efgh abcd efgh abcd efgh
abcd efgh abcd efgh abcd efgh
</textarea>
<br/>
<input type="button" value="Select text" onclick="select_field('textarea1')">
</form>