Question

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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

Answer 1

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);

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Update(based on comments): Why doesn’t this work on “large numbers”?

For the primitive type Number, the safest max value is 2^53-1(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);

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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