What is the difference between regular (JS) Re = new Regexp ("^ \ D * $") and Re =/^ \ D * $?

Below CodeResult: false, true, true
Why is the first result false?
<Form name = form1>
String: <input name = "T1" value = "123456">
Mode:/<input name = "T2" value = "^ \ D * $">/
</Form>
<Script language = JavaScript>
Function C1 ()
{
Re = new Regexp ("^ \ D * $ ");
Alert (Re. Test ("123456 "));
}
Function C2 (form)
{
Re = new Regexp (Form. t2.value );
Alert (Re. Test (Form. t1.value ));
}
Function C3 ()
{
Re =/^ \ D * $ /;
Alert (Re. Test ("123456 "));
}
C1 ();
C2 (document. form1 );
C3 ();
</SCRIPT>
The first should beRe = new Regexp ("^ \ D * $ ");
\ Escape in quotation marks
The first pair has double quotation marks. The double quotation marks must be escaped once. The second pair does not exist. This is the difference.