A small wrapper around Typescript's tsserver for easier scripting

simple-tsserver-script.js

// @ts-check
const childProcess = require('child_process');
const path = require('path');
const TTL_MS = 5000;

/**
 * @description Start a connection to tsserver
 * @param {{debug?: boolean}} options
 * @example
    const chat = tsserverAPI.start();
    await chat.read(msg => msg.event === 'typingsInstallerPid');
    chat.send({
      type: 'request',
      command: 'open',
      arguments: {
        file: '/path/to/file.ts'
      }
    });
    await chat.read(msg => msg.event === 'projectLoadingFinish');
    const reply = await chat.send({
      type: 'request',
      command: 'implementation',
      arguments: {
        file: '/path/to/file.ts',
        line: 6,
        offset: 24
      }
    });
    console.log(reply);
 */
function start({debug} = {}) {
    const tsserverPath = path.join(path.dirname(require.resolve('typescript')), 'tsserver.js');
    const proc = childProcess.fork(tsserverPath, [], {silent: true});
    const unreadMessages = new Set();
    const waitingReaders = new Set();

    let readBuffer = '';
    proc.stdout.on('data', buffer => {
        readBuffer += buffer.toString('utf8');
        const lines = readBuffer.split('\n');
        readBuffer = '';

        for (const line of lines) {
            if (line.startsWith('{')) {
                try {
                    const msg = JSON.parse(line);
                    if (debug) {
                        console.debug('>>', msg);
                    }
                    unreadMessages.add(msg);
                    setTimeout(() => {
                        unreadMessages.delete(msg);
                    }, TTL_MS);
                    waitingReaders.forEach(asleepReader => {
                        asleepReader();
                    });
                } catch {
                    readBuffer = line;
                    continue;
                }
            }
        }
    });

    let seq = 0;

    /**
     * @description Send 'msg' to the tsserver process
     * @param {object} msg
     * @returns {Promise<object>} The reponse from tsserver
     */
    async function send(msg) {
        const msgSeq = (msg.seq = ++seq);
        proc.stdin.write(JSON.stringify(msg) + '\n');
        return read(msg => msg.request_seq === msgSeq);
    }

    /**
     * @description read the next message that matches 'condition'
     * @param {Function} condition
     * @returns {Promise<object>} the matched message
     */
    async function read(condition) {
        return new Promise(resolve => {
            function reader() {
                for (const msg of unreadMessages.values()) {
                    if (condition(msg)) {
                        unreadMessages.delete(msg);
                        waitingReaders.delete(reader);
                        resolve(msg);
                        break;
                    }
                }
            }
            reader();
            waitingReaders.add(reader);
        });
    }

    return {
        send,
        read
    };
}

module.exports = exports = {
    start
};