TypeScript Compiler API - Example

ts-compile.ts

// TypeScript code to programatically run the equivalent of `tsc`
//
// With Slight modifications, such as *Colorized* output being displayed.
//
// However, the nice one-line Error Summary that `tsc` gives you (e.g. Errors in X files) is currently missing.
//
// Refs:
//   - https://github.com/microsoft/TypeScript-wiki/blob/main/Using-the-Compiler-API.md
//   - https://github.com/Microsoft/TypeScript/issues/6387#issuecomment-169739615

import { readFileSync } from 'node:fs';
import { dirname } from 'node:path';
import { exit } from 'process';
import ts from 'typescript';

// TODO
const rootDir = '.';

const {
    useCaseSensitiveFileNames,
    // getCurrentDirectory,
    newLine,
} = ts.sys;

const getCanonicalPath: (path: string) => string =
    useCaseSensitiveFileNames ? (v) => v : (v) => v.toLowerCase();

function getNewLine(): string {
    return newLine;
}

function reportDiagnostics(
    diagnostics: ts.Diagnostic[],
    curDir = rootDir
) {
    if (diagnostics.length == 0) return;

    const formatDiagnosticsHost: ts.FormatDiagnosticsHost = {
        getCurrentDirectory: () => curDir,
        getCanonicalFileName: getCanonicalPath,
        getNewLine: getNewLine,
    };

    // De-duplicate diagnostics, as mentioned here:
    //   https://github.com/microsoft/TypeScript/issues/20876
    const allDiagnostics =
        ts.sortAndDeduplicateDiagnostics(diagnostics);

    console.log(
        ts.formatDiagnosticsWithColorAndContext(
            allDiagnostics,
            formatDiagnosticsHost
        )
    );

    // allDiagnostics.forEach((diagnostic) => {
    //     if (diagnostic.file) {
    //         const { line, character } =
    //             diagnostic.file.getLineAndCharacterOfPosition(
    //                 diagnostic.start!
    //             );
    //         const message = ts.flattenDiagnosticMessageText(
    //             diagnostic.messageText,
    //             '\n'
    //         );
    //         console.log(
    //             `${diagnostic.file.fileName} (${line + 1},${
    //                 character + 1
    //             }): ${message}`
    //         );
    //     } else {
    //         console.log(
    //             ts.flattenDiagnosticMessageText(
    //                 diagnostic.messageText,
    //                 '\n'
    //             )
    //         );
    //     }
    // });
}

function readConfigFile(configFileName: string) {
    // Read config file
    const configFileText = readFileSync(configFileName).toString();

    // Parse JSON, after removing comments. Just fancier JSON.parse
    const result = ts.parseConfigFileTextToJson(
        configFileName,
        configFileText
    );
    const configObject = result.config;
    if (!configObject) {
        reportDiagnostics([result.error!]);
        exit(1);
    }

    // Extract config infromation
    const configParseResult = ts.parseJsonConfigFileContent(
        configObject,
        ts.sys,
        dirname(configFileName)
    );
    if (configParseResult.errors.length > 0) {
        reportDiagnostics(configParseResult.errors);
        exit(1);
    }
    return configParseResult;
}

const compile = (configFileName: string) => {
    // Extract configuration from config file
    const config = readConfigFile(configFileName);

    // Compile
    const program = ts.createProgram(
        config.fileNames,
        config.options
    );
    const emitResult = program.emit();

    const allDiagnostics = ts
        .getPreEmitDiagnostics(program)
        .concat(emitResult.diagnostics);

    // Report errors
    reportDiagnostics(allDiagnostics);

    // Check return code
    if (emitResult.emitSkipped) {
        const exitCode = 1;
        console.log(`Process exiting with code '${exitCode}'.`);
        exit(exitCode);
    }
};

// TODO
compile(process.argv[2]);

// run with:
//    npx ts-node ts-compile.ts tsconfig.json