如何将以零开头的十进制数转换为字符串

Question

Is there any way to turn a base ten number with leading zeroes into a string in javascript? It seems as if javascript just doesn't have the concept of a base ten number with leading zeroes.

Example of what I want

function turnBaseTenNumberToString(num) {
  ...
}

console.log(turnBaseTenNumberToString(010));
// outputs
// '010'

I should note the following does not work
Number.prototype.toString(<radix>)

console.log((010).toString(10))
// outputs
// '8'

which I assume is the result of the number evaluating prior to calling toString.

Answer 1

The problem is that decimal integer literals can't have leading zeros:

DecimalIntegerLiteral ::
    0
    NonZeroDigit DecimalDigits(opt)

However, ECMAScript 3 allowed (as an optional extension) to parse literals with leading zeros in base 8:

OctalIntegerLiteral ::
    0 OctalDigit
    OctalIntegerLiteral OctalDigit

But ECMAScript 5 forbade doing that in strict-mode:

A conforming implementation, when processing strict mode code (see 10.1.1) , must not extend the syntax of NumericLiteral to include OctalIntegerLiteral as described in B.1.1 .

ECMAScript 6 introduces BinaryIntegerLiteral and OctalIntegerLiteral , so now we have more coherent literals:

• BinaryIntegerLiteral , prefixed with 0b or 0B .
• OctalIntegerLiteral , prefixed with 0o or 0O .
• HexIntegerLiteral , prefixed with 0x or 0X .

The old OctalIntegerLiteral extension has been renamed to LegacyOctalIntegerLiteral , which is still allowed in non-strict mode.

Therefore, 010 is a syntax error, which may be tolerated by some browsers only in non-strict mode. But you can't rely on that, and even then it will produce the number 8 .

Answer 2

As per OP

turn a base ten number with leading zeroes into a string

Well, JavaScript treats a leading zero as an indicator that the value is in base 8. Thus when defining number as 010 the number value in decimal system is 8 (1 * 8^1 + 0 * 8^0) .

If you want to avoid that, you should pass a number in string representation and remove a leading zero if needed.

 function turnBaseTenStringToNumber(num) { return parseInt(num.replace(/^0+/, '')); } console.log(turnBaseTenStringToNumber(`010`)); // outputs 10 

See number with radix documentation for more details.