@eternaljs/captcha/src/index.ts

This npm package generates secure and customizable CAPTCHA images for web applications, preventing automated abuse with ease.

import { createCanvas } from 'canvas';
import { CaptchaInterface, OptionsInterface } from './interface';

function generateCaptcha(options: OptionsInterface): CaptchaInterface {
    const canvas = createCanvas(options['width'], options['height']);
    const ctx = canvas.getContext('2d');

    const captchaText = generateCaptchaText(options['length'] ?? 6);

    ctx.font = `${options['font_size']}px Arial`;
    ctx.textBaseline = 'middle';
    ctx.textAlign = 'center';

    const textX = options['width'] / 2;
    const textY = options['height'] / 2;

    ctx.fillText(captchaText, textX, textY);

    ctx.beginPath();
    ctx.moveTo(textX - ctx.measureText(captchaText).width / 2, textY);
    ctx.lineTo(textX + ctx.measureText(captchaText).width / 2, textY);
    ctx.strokeStyle = 'rgba(0,0,0)';
    ctx.stroke();

    const lines: number = options['lines'] ?? 6
    for (let i = 0; i < lines; i++) {
        ctx.beginPath();
        ctx.moveTo(0, Math.random() * options['height']);
        ctx.lineTo(options['width'], Math.random() * options['height']);
        ctx.strokeStyle = 'rgba(0,0,0,0.8)';
        ctx.stroke();
    }

    return { text: captchaText, image: canvas, };
}

function generateCaptchaText(length: number): string {
    const charSet: Record<string, string> = {
        digit: '0123456789',
        lowercase: 'abcdefghijklmnopqrstuvwxyz',
        uppercase: 'ABCDEFGHIJKLMNOPQRSTUVWXYZ',
    }

    let captchaText = '';

    for (const type in charSet) {
        captchaText += charSet[type].charAt(Math.floor(Math.random() * charSet[type].length));
    }

    const remaining: number = length - captchaText.length;

    if (!remaining) return captchaText;

    for (let i = 0; i < remaining; i++) {
        if (i === 0) {
            captchaText += charSet["uppercase"].charAt(Math.floor(Math.random() * charSet["uppercase"].length));
        } else if (i === 1) {
            captchaText += charSet["lowercase"].charAt(Math.floor(Math.random() * charSet["lowercase"].length));
        } else {
            captchaText += charSet["digit"].charAt(Math.floor(Math.random() * charSet["digit"].length));
        }
    }

    return captchaText.split('').sort(() => Math.random() - 0.5).join('');
}

export default generateCaptcha;