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How to Remove Leading Zeros from a String in JavaScript

When dealing with data like version numbers, serial numbers, or formatted IDs, you often encounter strings with leading zeros (e.g., "007"). A common task is to remove these zeros, either to get the clean numeric value or to reformat the string.

This guide will demonstrate the two main approaches to this problem. We'll cover the string manipulation method using replace() with a regular expression, and the type conversion method using Number() or parseInt(), explaining the crucial differences between them.

The Core Task: String Manipulation vs. Type Conversion​

It's important to decide on your goal:

  • String Manipulation: Do you want to get a new string with the zeros removed? (e.g., "007" -> "7")
  • Type Conversion: Do you want to get the number value that the string represents? (e.g., "007" -> 7)

The best method depends on your desired output type.

If your goal is to get a string without the leading zeros, the String.prototype.replace() method with a simple regular expression is the most direct and robust solution.

Problem: you have a string and you want to remove any zeros from the beginning.

// Problem: Convert "00123" to "123" as a string.
let idString = '00123';

Solution:

function removeLeadingZeros(str) {
  // The regex /^0+/ matches one or more zeros at the start of the string.
  return str.replace(/^0+/, '');
}

// Example Usage:
let idString = '00123';
let trimmedString = removeLeadingZeros(idString);

console.log(trimmedString);         // Output: "123"
console.log(typeof trimmedString);  // Output: string
note

This is the recommended best practice if you want the output to remain a string.

Solution 2 (For Number Conversion): Using Number() or parseInt()​

If your goal is to get the actual number value from the string, the simplest way is to use a type conversion function like Number() or parseInt(). These functions automatically discard leading zeros during the parsing process.

let idString = '00123';

// The Number() constructor is the cleanest way to convert.
let numberValue = Number(idString);

console.log(numberValue);         // Output: 123
console.log(typeof numberValue);  // Output: number

// parseInt() is also a great option, especially if you need to specify a radix.
let numberValueFromInt = parseInt(idString, 10);
console.log(numberValueFromInt);  // Output: 123

Output:

123
number
123
note

This is the recommended best practice if your final goal is to get a number for use in calculations.

note

Unary Plus Operator (+): A concise shorthand for Number() is the unary plus operator.

let numberValue = +'00123';
console.log(numberValue);   // Output: 123

How the Regular Expression Works​

The regular expression /^0+/ is the key to the string manipulation method.

  • / ... /: The delimiters for the regular expression.
  • ^: This is an "anchor." It asserts that the pattern must occur at the beginning of the string.
  • 0: Matches the literal character 0.
  • +: This is a "quantifier." It matches the preceding character (0) one or more times.

So, /^0+/ translates to: "Find one or more zeros that are located at the very start of the string." The replace() method then replaces this match with an empty string, effectively deleting the leading zeros.

A Note on Floating-Point Numbers​

Both methods handle floating-point numbers correctly.

  • replace(): The regex /^0+/ will stop at the decimal point, preserving the fractional part. 
    '0012.34'.replace(/^0+/, '');   // Output: "12.34"
  • Number() and parseFloat(): These functions are designed to parse floating-point numbers correctly. 
    Number('0012.34');              // Output: 12.34
    parseFloat('0012.34');          // Output: 12.34

Conclusion​

Removing leading zeros from a string is a simple task, and the best method depends on your desired output type.

  • If you want to get a string with the leading zeros removed, the recommended best practice is to use replace() with a regular expression: str.replace(/^0+/, '').
  • If you want to convert the string into a number, the cleanest and most direct method is the Number() constructor: let num = Number(str).

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