Bogus char in Javascript testcase: all breaks

Question

I'm using a JavaScript library called phpjs The goal is to create functions that mimic how PHP handles them.

Here's one function in particular: http://phpjs.org/functions/is_float:442

I've written a couple of test-cases and all is as expected. However, all breaks when I try this:

document.write(is_float(16.0x00000000));

No true or false hits the screen, just empty white space. Why is this?

While I'm at it, in that function, it says return !!(mixed_var % 1); What is the double !! for? I've never encountered this before. Leaving one out in the source code gets the exact same result for the following test-cases. Any case I might be forgetting?

document.write(is_float(186.31));document.write('<br>');
document.write(is_float("186.31"));document.write('<br>');
document.write(is_float("number"));document.write('<br>');
document.write(is_float("16.0x00000000"));document.write('<br>');
document.write(is_float("16"));document.write('<br>');
document.write(is_float(16));document.write('<br>');
document.write(is_float(0));document.write('<br>');
document.write(is_float("0"));document.write('<br>');
document.write(is_float(0.0));document.write('<br>');
document.write(is_float("0.0"));document.write('<br>');
document.write(is_float("true"));document.write('<br>');
document.write(is_float(true));document.write('<br>');
document.write(is_float("false"));document.write('<br>');
document.write(is_float(false));document.write('<br>');

EDIT: about the 0.0 issue, this cannot be fixed. Check the documentation:

//1.0 is simplified to 1 before it can be accessed by the function, this makes
//it different from the PHP implementation. We can't fix this unfortunately.

It appears that this is just something that JavaScript does, on it's own. The programmer has no control over this.

Answer 1

16.0x00000000 is not a valid numeric expression in JavaScript. If you are trying to express a hexidecimal value, the proper notation is 0x16 (22 in base 10) and decimals are not allowed. If, by chance, you are trying to express a value using scientific notation, the proper notation is 1.632e2 (163.2).

!! is a trick to convert to boolean. Consider !!0, which can be interpreted as !(!0). It first becomes true, which of course is not accurate, then goes back to false which is the correct boolean representation for 0.

Answer 2

"0x...." is javascript notation for a hexidecimal number. However, 16.0x0000 cannot be interpreted as anything meaningful. typeof 16.0x00 is throwing a Javascript error. This is expected. What you really want is is_float(0x16) or something similar

It sounds like you're validating input. If you truly want to test that something entered (in a text field, for example) is actually a float, I would suggest creating your own function like:

function is_float(input) {
    if (typeof input !== 'string') {
        input = input.toString();
    }
    return /^\-?\d{1,9}\.\d+$/.test(input);
}

is_float("16.0x00"); //false
is_float("16.00");   //true

That way you don't have to deal with converting numbers etc.

Answer 3

To skip Syntax Error, I think only way is to put it in try catch and eval it like this.

try{eval("document.write(is_float(16.0x00000000));")}catch(e){}

But its kind of weird way, better put try catch in is_float function and accept only strings like "16.0x00000" not 16.0x00000.