ts_watcher.ts

import * as ts from 'typescript';
const watchCompilerHost = ts.createWatchCompilerHost(
    ['index.ts'],
    {strict: true, target: ts.ScriptTarget.ESNext},
    ts.sys,
);
const originalCreateProgram = watchCompilerHost.createProgram;
watchCompilerHost.watchFile = (path, callback) => {
    // console.log('watchFile', path);
    return {
        close() {},
    };
};
watchCompilerHost.onWatchStatusChange = () => {
    console.log('Updates');
};
const origAfterProgramCreate = watchCompilerHost.afterProgramCreate;
watchCompilerHost.afterProgramCreate = p => {
    origAfterProgramCreate!(p);
    console.log('done');
};
watchCompilerHost.createProgram = (...args) => {
    const compilerHost = args[2]!;
    compilerHost.writeFile = file => {
        console.log('write', file);
    };
    return originalCreateProgram(...args);
};
const builder = ts.createWatchProgram(watchCompilerHost);

setTimeout(() => {
    builder.updateRootFileNames(['x.ts']);
}, 2000);