JS点击文字后变为输入框编辑

<span id="it1">内容</span> <a href="javascript:;" id="a1" onclick="cg(this)">修改</a>

<span id="it2">内容</span> <a href="javascript:;" id="a2" onclick="cg(this)">修改</a>

<span id="it3">内容</span> <a href="javascript:;" id="a3" onclick="cg(this)">修改</a>

<span id="it4">内容</span> <a href="javascript:;" id="a4" onclick="cg(this)">修改</a>

<span id="it5">内容</span> <a href="javascript:;" id="a5" onclick="cg(this)">修改</a>

<script>

cg = function (obj) {

var o = document.getElementById("it" + obj.id.toString().substr(1));

if (o.childNodes[0].value) {

o.innerHTML = o.childNodes[0].value;

} else {

o.innerHTML = "<input type='text' value='" + document.getElementById("it" + obj.id.toString().substr(

1)).innerHTML + "' />";

}

}

</script>