TypeScript Compiler API: Check language syntax using string content

check-syntax.ts

import ts from "typescript";

const code = `type A = string;`;
const sourceFile = ts.createSourceFile("source.ts", code, ts.ScriptTarget.Latest);
const host = ts.createCompilerHost({});
const getSourceFile = host.getSourceFile;
host.getSourceFile = function (name, languageVersion) {
  return name === sourceFile.fileName ? sourceFile : getSourceFile.call(host, name, languageVersion);
};
const program = ts.createProgram([sourceFile.fileName], { noEmit: true }, host);
const diagnostics = ts.getPreEmitDiagnostics(program);
if (diagnostics.length > 0) {
  console.error("Syntax errors found:");
  diagnostics.forEach((diagnostic) => {
    if (!diagnostic.start) return;
    if (!diagnostic.file) return;
    const { line, character } = diagnostic.file.getLineAndCharacterOfPosition(diagnostic.start);
    const message = ts.flattenDiagnosticMessageText(diagnostic.messageText, "\n");
    console.error(`  Error at ${diagnostic.file.fileName} (${line + 1},${character + 1}): ${message}`);
  });
}