Casting

[iwato]

QUESTION: How does one convert a string variable to a number variable for the purpose of numerical comparison?BACKGROUND: In Flash's ActionScript it was possible to cast a string-type variable as a number-type variable to facilitate numerical comparisons. How does one go about this in Javascript?Roddy

[Ingolme]

You can use Number().

var x = "3";var y = "2" + x;var result = Number(y) + Number(x);alert(result); // Alerts "26"

But if you're not performing a sum (summing and concatenating use the same operator), you will be able to operate with them and the type will change automatically:

var x = "2";var y = "2" + x;var result = y * x;alert(result); // Alerts "44"

[iwato]

You can use Number().Thank you for alerting me to the use of the Number() function. By way of confirmation are you saying that for all x and y whose values are numbers expressed as strings the following is true?

x > y == Number(x) > Number(y)

Roddy

[Ingolme]

Yes, that is correct.Since Javascript is a very forgiving language, it will convert types wherever it is necessary.if ("89" < "501") is just the same as writing if(89 < 501)

[iwato]

Yes, that is correct.It is a small kindness, but the sentence "Breaking any of these rules will result in a warn from an administrator, and may ultimately result in being banned." at Rings and Emeralds would read more easily, if you wrote "Breaking any of these rules will result in a warning from an administrator and the possibility of your being banned."I watched one of your games. Nicely done!Roddy

[justsomeguy]

It's usually better to convert and then check for an error before trying to use the values. You can use parseFloat and isNaN to do that.

var x = "123";var y = "xyz";x = parseFloat(x, 10);y = parseFloat(y, 10);if (isNaN(x))  alert("x is not a number");else if (isNaN(y))  alert("y is not a number");else  alert(x + y);

[iwato]

It's usually better to convert and then check for an error before trying to use the values. You can use parseFloat and isNaN to do that.

var x = "123";var y = "xyz";x = parseFloat(x, 10);y = parseFloat(y, 10);

Yes, I had forgotten about the parseFloat() method, perhaps because of its complexity and specificity to more sophisticated mathematical manipulations. In any case, as Ingolme explained, when making a comparison even strings are permissible.

if (isNaN(x))  alert("x is not a number");else if (isNaN(y))  alert("y is not a number");else  alert(x + y);

So, why do you not use the try, throw and catch construct? My comparison, by the way, is made in just such a pattern, and it works great. You can use the same error message over.

[Synook]

So, why do you not use the try, throw and catch construct?

Very slow. Benchmark it! :)parseFloat() isn't really just for "sophisticated mathematical manipulations", just for when you may be dealing with non-integers.

[jesh]

Very slow. Benchmark it!

parseInt(), if you are really looking for integers rather than floats, is even faster still:

<script type="text/javascript">var start;start = new Date();for(var i = 0; i < 1000000; i++){	parseFloat(i,10);}document.write(new Date() - start);document.write("<br />");start = new Date();for(var i = 0; i < 1000000; i++){	parseInt(i,10);}document.write(new Date() - start);document.write("<br />");</script>

About 4 times faster on my machine - 400ms for one million parseFloats and 100ms for one million parseInts.

[Synook]

I was actually thinking of try...catch v. conditionals but good point, anyway.

[jeffman]

Well, next time I need to parse a million integers . . .