locutus/esm/c/stdlib/strtod.js

Locutus other languages' standard libraries to JavaScript for fun and educational purposes

export function strtod(str) {
    //      discuss at: https://locutus.io/c/stdlib/strtod/
    // parity verified: C 23
    //     original by: Kevin van Zonneveld (https://kvz.io)
    //          note 1: Parses a floating-point number from the start of the string.
    //          note 2: Stops at the first invalid trailing character, similar to C strtod.
    //       example 1: strtod('3.14')
    //       returns 1: 3.14
    //       example 2: strtod('  -2.5e2xyz')
    //       returns 2: -250
    //       example 3: strtod('abc')
    //       returns 3: 0
    const input = String(str).replace(/^\s+/, '');
    const match = input.match(/^[+-]?(?:\d+\.?\d*|\.\d+)(?:[eE][+-]?\d+)?/);
    if (!match || !match[0]) {
        return 0;
    }
    const parsed = Number.parseFloat(match[0]);
    return Number.isNaN(parsed) ? 0 : parsed;
}