Convert the string of any base to integer in JavaScript

The parseInt() function in JavaScript converts strings representing numbers in any base (2-36) to decimal integers. This is useful when working with binary, octal, hexadecimal, or other numeral systems.

Syntax

parseInt(string, radix);

Parameters

string ? The value to parse. If not a string, it's converted using the ToString method. Leading whitespace is ignored.

radix ? An integer between 2 and 36 representing the base of the numeral system. If omitted, defaults to 10 (except for strings starting with "0x" which default to 16).

Examples

Converting Different Bases to Decimal

console.log(parseInt("100", 10));    // Decimal (base 10)
console.log(parseInt("10", 8));      // Octal (base 8)
console.log(parseInt("101", 2));     // Binary (base 2)
console.log(parseInt("2FF3", 16));   // Hexadecimal (base 16)
console.log(parseInt("ZZ", 36));     // Base 36 (max base)

100
8
5
12275
1295

Common Base Conversions

// Binary to decimal
console.log(parseInt("1010", 2));    // 10

// Hexadecimal to decimal  
console.log(parseInt("FF", 16));     // 255
console.log(parseInt("A1", 16));     // 161

// Octal to decimal
console.log(parseInt("777", 8));     // 511

10
255
161
511

Edge Cases and Important Notes

// Leading whitespace ignored
console.log(parseInt("  42", 10));   // 42

// Stops parsing at first invalid character
console.log(parseInt("123abc", 10)); // 123

// Returns NaN for invalid input
console.log(parseInt("xyz", 10));    // NaN

// Always specify radix to avoid confusion
console.log(parseInt("010", 8));     // 8 (octal)
console.log(parseInt("010", 10));    // 10 (decimal)

42
123
NaN
8
10

Key Points

• Always specify the radix parameter to avoid unexpected behavior
• Valid digits depend on the base: binary (0-1), octal (0-7), decimal (0-9), hex (0-9, A-F)
• Base 36 uses digits 0-9 and letters A-Z (case insensitive)
• Parsing stops at the first invalid character for the specified base
• Returns NaN if no valid number can be parsed

Conclusion

The parseInt() function with a specified radix parameter is the standard way to convert strings from any base (2-36) to decimal integers. Always include the radix parameter for predictable results.