javascript if number greater than number

Question

I have this javascript function to validate if a number is greater than another number

function validateForm() {
    var x = document.forms["frmOrder"]["txtTotal"].value;
    var y = document.forms["frmOrder"]["totalpoints"].value;

    if (x > y) {
        alert("Sorry, you don't have enough points");
        return false;
    }
}

It's not working for some reason.

If I do alert(x) I get 1300, and alert(y) gives 999

This works....

function validateForm() {
    var x = 1300;
    var y = 999;

    if (x > y) {
        alert("Sorry, you don't have enough points");
        return false;
    }
}

@user1689607 Comparing numeric strings will still work, i.e `"5" > "2" // true` — Matt Stone, Oct 26 '12 at 01:32
@user1689607 `"user1689607" > "Matt Stone" // true` - I'll have to look up the exact rules for the string conversion. Strange that single digit number strings work correctly. — Matt Stone, Oct 26 '12 at 01:35
@MattStone, string comparison compares the strings letter by letter beginning with the first, `1` is less than `9`, which is why `'1300' < '999'`. — zzzzBov, Oct 26 '12 at 01:36
@MattStone: It's because the `"1"` character comes before the `"9"` character. It does the comparison in the same manner that it compares any other character. — I Hate Lazy, Oct 26 '12 at 01:36
Ah right, so it's still technically a string (ASCII order) comparison. Thanks guys. — Matt Stone, Oct 26 '12 at 01:38

xdazz · Accepted Answer · 2012-10-26T01:41:34.720

73

You should convert them to number before compare.

Try:

if (+x > +y) {
  //...
}

or

if (Number(x) > Number(y)) {
  // ...
}

Note: parseFloat and pareseInt(for compare integer, and you need to specify the radix) will give you NaN for an empty string, compare with NaN will always be false, If you don't want to treat empty string be 0, then you could use them.

edited Oct 26 '12 at 01:41

answered Oct 26 '12 at 01:34

xdazz

158,678
38
247
274

edrian · Answer 2 · 2016-09-30T13:58:00.500

3

You can "cast" to number using the Number constructor..

var number = new Number("8"); // 8 number

You can also call parseInt builtin function:

var number = parseInt("153"); // 153 number

edited Sep 30 '16 at 13:58

answered Oct 26 '12 at 01:36

edrian

4,501
5
31
35

Ooops, using Number as a constructor returns a Number object, and an object is only ever "equal" to itself, so `new Number('7') == new Number('7')` returns `false`. I think you meant to use it as a function, so `Number('7') == Number('7')`. And `parseInt` should always use a radix: `parseInt('153',10)`. – RobG Oct 26 '12 at 01:46
Ohh!, you are right @RobG about the "=="!! .. I tested these cases and were fine, and I suposed that Number object was always being calling "toString()" implicitly (actually, I think internally its calling valueOf() method): new Number('725') < new Number('800'); //Outputs true new Number('91') > new Number('90'); //Outputs true new Number('7') < new Number('7'); //Outputs false new Number('7') > new Number('8'); //Outputs false new Number('8') < new Number('7'); //Outputs false But for equals, in this way, you need: new Number('7').valueOf() == new Number('7').valueOf(); //Outputs true – edrian Oct 26 '12 at 03:22

score 3 · Answer 3 · answered Oct 26 '12 at 01:42

You're comparing strings. JavaScript compares the ASCII code for each character of the string.

To see why you get false, look at the charCodes:

"1300".charCodeAt(0);
49
"999".charCodeAt(0);
57

The comparison is false because, when comparing the strings, the character codes for 1 is not greater than that of 9.

The fix is to treat the strings as numbers. You can use a number of methods:

parseInt(string, radix)
parseInt("1300", 10);
> 1300 - notice the lack of quotes


+"1300"
> 1300


Number("1300")
> 1300

score 1 · Answer 4 · answered Oct 26 '12 at 01:34

1

Do this.

var x=parseInt(document.forms["frmOrder"]["txtTotal"].value);
var y=parseInt(document.forms["frmOrder"]["totalpoints"].value);

answered Oct 26 '12 at 01:34

specialscope

4,188
3
24
22

3

Specify that you want base 10 with `...]["txtTotal"].value, 10);` – Blender Oct 26 '12 at 01:34

javascript if number greater than number

4 Answers4

Linked

Related