Function to find string with only one emoji

How can I detect that the string only contains one emoji ? Now it returns true if it has any.

I want it only to be true if it contains only one emoji and nothing else.

function hasOneEmoji(str) {
    const regEx = /(?:[u2700-u27bf]|(?:ud83c[udde6-uddff]){2}|[ud800-udbff][udc00-udfff])[ufe0eufe0f]?(?:[u0300-u036fufe20-ufe23u20d0-u20f0]|ud83c[udffb-udfff])?(?:u200d(?:[^ud800-udfff]|(?:ud83c[udde6-uddff]){2}|[ud800-udbff][udc00-udfff])[ufe0eufe0f]?(?:[u0300-u036fufe20-ufe23u20d0-u20f0]|ud83c[udffb-udfff])?)*/g;

    if (str.match(regEx)) {
        return true;
    }

    return false;
}

function hasOneEmoji(str) {
  return /^(?:(?:[u2700-u27bf]|(?:ud83c[udde6-uddff]){2}|[ud800-udbff][udc00-udfff])[ufe0eufe0f]?(?:[u0300-u036fufe20-ufe23u20d0-u20f0]|ud83c[udffb-udfff])?(?:u200d(?:[^ud800-udfff]|(?:ud83c[udde6-uddff]){2}|[ud800-udbff][udc00-udfff])[ufe0eufe0f]?(?:[u0300-u036fufe20-ufe23u20d0-u20f0]|ud83c[udffb-udfff])?)*)$/.test(str);
}

console.log(hasOneEmoji('?'));
console.log(hasOneEmoji('?Hello'));
console.log(hasOneEmoji('Hello?'));
console.log(hasOneEmoji('??'));