怎么调用name="input[0]"的input,同样如果name="input.text1"的话又怎么调用

1<form name="form1">
2<input name="input[0]" type="text" value="test1"/>
3<script>   
4alert(form1.input[0]);//出错   
5</script>
6</form>

1<form name="form1">
2<input name="input[0]" type="text" value="test1"/>
3<script>   
4alert(document.getElementsByName("input[0]")[0].value);   
5</script>
6</form>

1<form name="form1">
2<input name="input[0]" type="text" value="test1"/>
3<script>   
4var a=document.getElementsByName("input[0]")   
5alert(a[0].value)   
6</script>
7</form>

1<form name="form1">
2<input id="input[0]" name="input[0]" type="text" value="test1"/>
3<script>   
4var a=document.getElementById("input[0]")   
5alert(a.value)   
6</script>
7</form>

1<form name="form1">
2<input id="input[0]" name="input[0]" type="text" value="test1"/>
3<script>   
4var a=document.getElementsByTagName("input")   
5alert(a[0].value)   
6</script>
7</form>