求助!script高手请进!!!

Question

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

Answer 1

<form name = form1>
<input type=text name="input[0]" value="test1"><script>
  var a=document.getElementsByName("input[0]")
  alert(a[0].value)
</script>
</form>

Answer 2

or <form name = form1>
<input type=text name="input[0]" id="input[0]" value="test1"><script>
  var a=document.getElementById("input[0]")
  alert(a.value)
</script>
</form>

Answer 3

or <form name = form1>
<input type=text name="input[0]" id="input[0]" value="test1"><script>
  var a=document.getElementsByTagName("input")
  alert(a[0].value)
</script>
</form>