点击按钮，将txt1的内容全部填入txt2中
<script>
function cal(){
var rem = document.getElementById('txt1').value;
document.getElementById('txt2').value = rem;
}
</script>
<form action="" method="get" name="myform">
<textarea cols="25" rows="8" id="txt1"></textarea>
<textarea cols="25" rows="8" id="txt2"></textarea>
<input name="" onClick="cal();" type="button" value="自动复制">
</form>
点击按钮，将剪切板内容自动粘贴到文本框中
