It works with a lot number types, but not with negatives hexadecimal or binary. Too, Number(octal) doesn't parse an octal number.

Number("15")    ===   15;  // OK
Number("-15")   ===  -15;  // OK
Number("0x10")  ===   16;  // OK
Number("0b10")  ===    2;  // OK
Number("-0x10") ===  NaN;  // FAIL (expect  -16)
Number("-0b10") ===  NaN;  // FAIL (expect   -2)
Number("0777")  ===  777;  // FAIL (expect  511)
Number("-0777") === -777;  // FAIL (expect -511)

Question: how I can parse all valid Javascript numbers correctly?

Edit A

parseInt() don't help me because I need check by each possibility (if start with 0x I use 16, for instance).

Edit B

If I write on Chrome console 0777 it turns to 511, and too allow negative values. Even works if I write directly into javascript code. So I expect basically a parser that works like javascript parser. But I think that the negative hexadecimal, for instance, on really is 0 - Number(hex) in the parser, and not literraly Number(-hex). But octal values make not sense.

It works with a lot number types, but not with negatives hexadecimal or binary. Too, Number(octal) doesn't parse an octal number.

Number("15")    ===   15;  // OK
Number("-15")   ===  -15;  // OK
Number("0x10")  ===   16;  // OK
Number("0b10")  ===    2;  // OK
Number("-0x10") ===  NaN;  // FAIL (expect  -16)
Number("-0b10") ===  NaN;  // FAIL (expect   -2)
Number("0777")  ===  777;  // FAIL (expect  511)
Number("-0777") === -777;  // FAIL (expect -511)

Question: how I can parse all valid Javascript numbers correctly?

Edit A

parseInt() don't help me because I need check by each possibility (if start with 0x I use 16, for instance).

Edit B

If I write on Chrome console 0777 it turns to 511, and too allow negative values. Even works if I write directly into javascript code. So I expect basically a parser that works like javascript parser. But I think that the negative hexadecimal, for instance, on really is 0 - Number(hex) in the parser, and not literraly Number(-hex). But octal values make not sense.

• javascript
• numbers

Share Improve this question Follow edited Mar 6, 2015 at 21:06 David Rodrigues asked Mar 6, 2015 at 20:40 David RodriguesDavid Rodrigues 12.6k1717 gold badges6666 silver badges9494 bronze badges 9

• 1 You could easily create your own function which inspects the first three characters of the string and handles it accordingly. – Felix Kling Commented Mar 6, 2015 at 20:45
• 5 parseInt() with the matching radix seems to work. – Sirko Commented Mar 6, 2015 at 20:45
• 2 parseInt("-0x10",16) gives you -16, and parseInt("-0777",8) gives you -511 – Matt Burland Commented Mar 6, 2015 at 20:45
• 1 Binary, octal, and hexidecimal literals have not been defined to support signs. Only a DecimalLiteral includes the syntax for SignedInteger. – Jonathan Lonowski Commented Mar 6, 2015 at 20:55
• 4 Regarding "Edit B:" Octal literals have changed in ES6 to 0o[0-7]+. The now "legacy" syntax of 0[0-7]+ only continues to be available when strict mode is not used. – Jonathan Lonowski Commented Mar 6, 2015 at 21:15

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4 Answers 4

Sorted by: Reset to default 3

Try this:

parseInt(string, base):

parseInt("-0777", 8) 
parseInt("-0x10", 16) 

You could write a function to handle the negative value.

function parseNumber (num) {
   var neg = num.search('-') > -1;
   var num = Number(num.replace('-', ''));
   return num * (neg ? -1 : 1);
}

It's not parsing octal and the other examples because they're not valid Javascript numbers, at least within the constraints of Number. So the technically correct answer is: use Number!

If you want to parse other formats, then you can use parseInt, but you will have to provide the base.

This gets a little ugly, but you could inspect the values to determine the right radix for parseInt. In particular, the b for binary doesn't seem to be support by my browser (Chrome) at all, so unlike the OP, Number("0b10") gives me NaN. So you need to remove the b for it to work at all.

var numbers = [
  "15", "-15", "0x10", "0b10", "-0x10", "-0b10", "0777", "-0777"
];

function parser(val) {
  if (val.indexOf("x") > 0) {
    // if we see an x we assume it's hex
    return parseInt(val, 16);
  } else if (val.indexOf("b") > 0) {
    // if we see a b we assume it's binary
    return parseInt(val.replace("b",""),2);
  } else if (val[0] === "0") {
    // if it has a leading 0, assume it's octal
    return parseInt(val, 8);
  }
  // anything else, we assume is decimal
  return parseInt(val, 10);
}

for (var i = 0; i < numbers.length; i++) {
  console.log(parser(numbers[i]));
}

Note this obviously isn't foolproof (for example, I'm checking for x but not X), but you can make it more robust if you need to.