nodejs script to run a watch mode typescript checker that can optionally output to json for consumption by other programs

watch.mjs

// Generated by Claude
// Some details hand tuned
import fs from 'fs'
import ts from 'typescript';
import path from 'path';

function getConfig() {
    const args = process.argv.slice(2);
    const jsonIndex = args.indexOf('--json');
    const useJson = jsonIndex !== -1;

    const paths = args.filter((arg, i) => !arg.startsWith('--') && i !== jsonIndex + 1);

    if (paths.length === 0) {
        paths.push('.');
    }

    const invalidPaths = paths.filter(p => !fs.existsSync(p));
    if (invalidPaths.length > 0) {
        console.error('Invalid paths:', invalidPaths.join(', '));
        process.exit(1);
    }

    return { paths, useJson };
}

const { paths, useJson } = getConfig();

let cwd = process.cwd()

function watchProgram(rootFiles) {
    const configPath = ts.findConfigFile(cwd, ts.sys.fileExists, "tsconfig.json");
    if (!configPath) throw new Error("tsconfig.json not found");

    const host = ts.createWatchCompilerHost(
        configPath,
        { noEmit: true },
        ts.sys,
        ts.createSemanticDiagnosticsBuilderProgram,
        reportDiagnostic,
        reportWatchStatus,
    );

    ts.createWatchProgram(host);
}

function categoryLabel(category) {
    switch (category) {
        case 0: return "warning"
        case 1: return "error"
        case 2: return "suggestion"
        case 3: return "message"
    }
}

function reportDiagnostic(diagnostic) {
    if (!diagnostic.file) return;

    const { line, character } = diagnostic.file.getLineAndCharacterOfPosition(diagnostic.start);
    const message = ts.flattenDiagnosticMessageText(diagnostic.messageText, "\n");

    let category = categoryLabel(diagnostic.category)
    let time = formatDate(new Date())
    let fileName = path.relative(cwd, diagnostic.file.fileName)
    if (diagnostic.category === 1) { // error
        if (useJson) {
            console.log(JSON.stringify({
                time,
                category,
                fileName,
                line: line+1,
                character: character+1,
                code: diagnostic.code,
                message,
            }))

        } else {
            console.log(`${time} ${category} TS${diagnostic.code} ${fileName}:${line+1}:${character+1}`);
            console.log(message)
        }
    }
}

// Generated by Claude
function formatDate(date) {
    const pad = n => n.toString().padStart(2, '0');

    const year = date.getFullYear();
    const month = pad(date.getMonth() + 1);
    const day = pad(date.getDate());
    const hour = pad(date.getHours());
    const minute = pad(date.getMinutes());
    const second = pad(date.getSeconds());

    return `${year}-${month}-${day} ${hour}:${minute}:${second}`;
}

function reportWatchStatus(diagnostic) {
    /*
    if (useJson) {
        console.log("{}")
    } else {
        console.log("----", formatDate(new Date()))
    }
    */
}

watchProgram(paths);