if(document.getElementById("myElmentID").classList.contains("hidden")){
// I have the 'hidden' class
}

const element = document.querySelector("#box");
element.classList.contains("active");

if (typeof maybeObject != "undefined") { alert("It exists!");
}

var isMobileVersion = document.getElementsByClassName('snake--mobile');
if (isMobileVersion.length > 0) { // elements with class "snake--mobile" exist
}

{"tags":[{"tag":"textarea","content":"expect(elem.contains('foo')).toBe(true); \/\/expect elem to contain class foo\n\/\/ Use above if at least this class is expected to be included.\n\/\/ If an exact series of classes are expected to be in elem use below\nexpect(elem).toHaveClass(\"class1 class2\");","code_language":"javascript"}]}

 const div = document.querySelector('.info');
div.classList.contains('secondary'); // trueCode language: JavaScript (javascript)

if (typeof me.onChange !== "undefined") { // safe to use the function me.onChange()
}
//or better yet
if (typeof me.onChange === "function") { // safe to use the function me.onChange()
}

 <div class="secondary info">Item</div>Code language: HTML, XML (xml)

export const isClass = <T>(value: unknown): value is Constructor<T> => {	return typeof value === "function" && typeof value.prototype === "object";
};
export type Constructor<T> = new (...args: unknown[]) => T;