Gulp + TSC hack

gulpfile.js

let isWatching = false;

gulp.task('ts', () => {
    return new Promise((resolve, reject) => {
        const cmd = 'npx';
        const args = ['tsc'];

        if (isWatching) {
            args.push('-w', '--preserveWatchOutput');
        }

        const tsc = spawn(cmd, args);
        const sanitizeTSCOutput = (data) => data.toString().trim();

        tsc.stdout.on('data', (data) => {
            const message = sanitizeTSCOutput(data);
            log(message);

            // Hack to let gulp know we have the watcher online
            if (isWatching && message.includes('Watching for file changes')) {
                resolve();
            }
        });

        tsc.stderr.on('data', (data) => {
            log(sanitizeTSCOutput(data));
        });

        tsc.on('error', log);

        tsc.on('close', (code) => {
            if (!isWatching) {
                code !== 0 ? reject('TSC failed') : resolve();
            }
        });
    });
});

gulp.task('watch', gulp.series(function setIsWatching(cb) {
    isWatching = true;
    cb();
}, 'ts'));

Very intersting! I'd like to do something similar in my project to speed up incremental compilation. How do you call this? And how to ensure it uses tsc version that was downloaded with npm?

ping