Remove leading zeros from a number in Javascript [duplicate]

2020/11/16 01:41 · javascript ·  · 0评论

Possible Duplicate:
Truncate leading zeros of a string in Javascript

What is the simplest and cross-browser compatible way to remove leading zeros from a number in Javascript ?

e.g. If I have a textbox value as 014 or 065, it should only return 14 or 65

We can use four methods for this conversion

  1. parseInt with radix 10
  2. Number Constructor
  3. Unary Plus Operator
  4. Using mathematical functions (subtraction)
const numString = "065";

//parseInt with radix=10
let number = parseInt(numString, 10);
console.log(number);

// Number constructor
number = Number(numString);
console.log(number);

// unary plus operator
number = +numString;
console.log(number);

// conversion using mathematical function (subtraction)
number = numString - 0;
console.log(number);


Update(based on comments): Why doesn't this work on "large numbers"?

For the primitive type Number, the safest max value is 253-1(Number.MAX_SAFE_INTEGER).

console.log(Number.MAX_SAFE_INTEGER);

Now, lets consider the number string '099999999999999999999' and try to convert it using the above methods

const numString = '099999999999999999999';

let parsedNumber = parseInt(numString, 10);
console.log(`parseInt(radix=10) result: ${parsedNumber}`);

parsedNumber = Number(numString);
console.log(`Number conversion result: ${parsedNumber}`);

parsedNumber = +numString;
console.log(`Appending Unary plus operator result: ${parsedNumber}`);

parsedNumber = numString - 0;
console.log(`Subtracting zero conversion result: ${parsedNumber}`);

All results will be incorrect.

That's because, when converted, the numString value is greater than Number.MAX_SAFE_INTEGER. i.e.,

99999999999999999999 > 9007199254740991

This means all operation performed with the assumption that the stringcan be converted to number type fails.

For numbers greater than 253, primitive BigInt has been added recently. Check browser compatibility of BigInthere.

The conversion code will be like this.

const numString = '099999999999999999999';
const number = BigInt(numString);

P.S: Why radix is important for parseInt?

If radix is undefined or 0 (or absent), JavaScript assumes the following:

  • If the input string begins with "0x" or "0X", radix is 16 (hexadecimal) and the remainder of the string is parsed
  • If the input string begins with "0", radix is eight (octal) or 10 (decimal)
  • If the input string begins with any other value, the radix is 10 (decimal)

Exactly which radix is chosen is implementation-dependent. ECMAScript 5 specifies that 10 (decimal) is used, but not all browsers support this yet.

For this reason, always specify a radix when using parseInt

regexp:

"014".replace(/^0+/, '')

It is not clear why you want to do this. If you want to get the correct numerical value, you could use unary + [docs]:

value = +value;

If you just want to format the text, then regex could be better. It depends on the values you are dealing with I'd say. If you only have integers, then

input.value = +input.value;

is fine as well. Of course it also works for float values, but depending on how many digits you have after the point, converting it to a number and back to a string could (at least for displaying) remove some.

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