제가 vscode 확장 기능인'search with qiita'를 만들어 봤어요.

let editor = vscode.window.activeTextEditor;
if (!editor) {
    vscode.window.showWarningMessage('No active text editor found!');
    return;
}

let extIndex: number = editor.document.fileName.lastIndexOf('.');
let lang: string = extIndex >= 0 ? editor.document.fileName.substring(extIndex + 1) : '';

private static defaultDocs : object = {
        "py": "python",
        "js": "javascript",
        "ts": "typescript",
        "kt": "kotlin",
        "rb": "ruby",
        "htm": "html",
        "cpp": "c++",
        "md": "markdown"
    };

public static getLang(ext: string, customDocs?: object): String {

    let docs : any = this.defaultDocs;
    // 足りない場合を考慮して、設定で追加できるようにする
    if (customDocs) {
        Object.assign(docs, customDocs);
    }

    if (ext in docs) {
        return docs[ext];
    } else {
        return ext;
    }
}