如何在javascript中使用substr

I have problem to case value from calendar value. Ex : Input text value from calendar = "2013-08-25" then the script case like this:

<script>
function convertDate() {
    var z = document.forms["form1"]["date_get"].value;
    var month = z.substring(5,7);

    switch (month) {
        case 01:
            x="I";
            break;
        case 02:
            x="II";
            break;
        case 03:
            x="III";
            break;
        case 04:
            x="IV";
            break;
        case 07:
            x="VII";
            break;
        case 08:
            x="VIII";
            break;
    }

    document.forms["form1"]["trans_code"].value = x;
}
</script>

Result Still I.

The case statements are not working.

Try:

case "01":
x="I";
break;
case "02":
x="II";
break;
etc...

Note that since you comparing Strings - those values 01, 02 etc need to be represented as Strings "01","02" etc.

If you provide 01 without the quotes it will be interpreted as 1 (integer), which is often taken to mean "true". That's why it accepts the first case.

You forgot the single or double quotes for string 01 02 03 ...

var z = '2013-08-25';
var month = z.substring(5,7);
var x = '';
switch (month)
{
    case '01':
        x="I";
        break;
    case '02':
        x="II";
        break;
    case '03':
        x="III";
        break;
    case '04':
        x="IV";
        break;
    case '07':
        x="VII";
        break;
    case '08':
        x="VIII";
        break;
    // etc.
}
alert(x);

use Quotes inside case statement like case "01"

A dict might be better than switch case:

var trans = {'01': 'I', '02': 'II'};
var month = '02';
alert(trans[month]);

see also: http://james.padolsey.com/javascript/how-to-avoid-switch-case-syndrome/

http://encosia.com/first-class-functions-as-an-alternative-to-javascripts-switch-statement/

https://coderwall.com/p/s7592q

Explicitly cast the substring into a number and be aware of octal notation in JavaScript for numbers starting with a zero.

<script>
function convertDate() {
    var z = document.forms["form1"]["date_get"].value;
    var month = +z.substring(5,7); //or parseInt(...)

    switch (month) {
        case 01:
            x="I";
            break;
        case 02:
            x="II";
            break;
        case 03:
            x="III";
            break;
        case 04:
            x="IV";
            break;
        case 07:
            x="VII";
            break;
        case 08:
            x="VIII";
            break;
    }

    document.forms["form1"]["trans_code"].value = x;
}
</script>