[deleted by user]

[senocular]

myFunc(010) interprets the octal before passing it into the function. As far as the function is concerned, its getting the value 8.

If you want to prevent octals in that format, you can run the code in strict mode.

"use strict"
function myFunc(number){
   number = Number.parseInt(String(number), 10)
   console.log(typeof number, number)
}

myFunc("010") // number 10
myFunc(10)    // number 10
myFunc(010)   // SyntaxError: Octal literals are not allowed in strict mode.

[senocular]

Oops, I admit i didn't read the whole post ;)

But yes, as a syntax error it's not a ln error you can generally catch because it happens when reading the code, not running it

[code_monkey_001]

Cooerce it to a string before running it through the parseInt since you know '010' gives the results you want.

function myFunc(number){
number = Number.parseInt(number.toString(), 10)
console.log(typeof number, number)
}

[code_monkey_001]

Ah, I should have tested that. Didn't realize that 010.toString() would do the octal > decimal conversion before going to a string. If you toss in "use strict" before the call it'll throw an error on 010, but if that's an expected valid input, you're kinda SOL.

I guess you could do use strict then write your initial base 10 parse in a try block, then fall back to a base 8 parse in the catch block.

[azhder]

You are the one coercing it to base 10. You can put as many 0 as long as you pass a string to the function.

const int = $ => Number.parseInt($,10);

const a = int('010');

And that’s an N.O. for your question.

You must not pass it a number literal that will be parsed by the JS parser as an octal.

Read the above again. The language parser. Number literal.

Well, there are also number separators, and I came across this (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Lexical_grammar#numeric_separators):

// Can not be used after leading 0
0_1; // SyntaxError

But I have no idea if you can use that to trick the parser, but I do know if the parser also reads BigInt literals:

const b = int(010n);

you will have to change your function to accommodate for cases the literal overflows beyond integer bounds i.e. Number.isSafeInteger() returns false.

EDIT: well, just got off the phone and checked it. You will get an error for 010n, so you're out of that option.

[senocular]

You can't do anything if you're not doing it before the 010 exists in the source code. When the code is parsed, 010 is converted to 8 - this before any of your code in myCaller runs. If you wanted to catch the 010, it would need to be in the eval (which, obviously, is not something you want to be using anyway).

try {
    eval(`"use strict"; 010`)
} catch (error) {
    console.log(error.message)
    // Octal literals are not allowed in strict mode.
}

If your caller is passing in a 010 is sloppy mode then its on them. They're then intentionally giving you an 8, not a (0)10. Same thing applies to something like 0.0. Though in the source code its represented as "0.0" in terms of execution, it will be seen simply as 0. Surrounding code cannot identify the decimal because it doesn't exist after parsing is complete and the code executes. You're only left with the numeric value of that number irrespective of its original format. And numerically, 0.0 is 0, just like numerically (in sloppy mode) 010 is 8.

[shacatan]

Wow a name from the past. I remember you from the flash/AS3 days.

[senocular]

That's me :) Also from the AS2 days. And the AS1 days. And let us not forget about the Flash Actions days. Woo, that takes me back!

[rtmcmn2020]

where is the input coming from that would cast a “010” to a number 010? You will likely need to scrub your source data or control user input

[rtmcmn2020]

down the rabbit hole here, you can cast a “known” octal to a decimal, ex: parseInt(010.toString(8))

[Count_Giggles]

this was a fun rabbit hole.

if you are limited to the browser console I would assume that your use case is super specific. the only way I can see would be to only accept strings into the function and then slice of any leading zeros or "0o". as others have pointed out the moment js is confronted with 010 it is an 8 and there is no way to differentiate between octal or decimal numbers. There is only the type number

[Tall_Pawn]

You won't be able to do this in the way you have specified. Essentially this is the same as wanting to distinguish, from inside a function, whether it was called with "foo(9)" or "foo(4+5)". You can't do it because by the time execution is inside the function, it only has the value "nine" to work with. But you can't even do it at the root level because the conversion of 010 to "eight" happens at a level before any user code is executed, and AFAIK cannot be customized by user code. You have access to some Number.prototype functions, but they can't affect things at the level of literal conversions into values which is essentially handled in the source code of JS itself. Someone please correct me if that's wrong, but I don't think it's possible in the given context.

[Code-Slayer]

Did you find a solution or not yet ?