How to know a javascript function exist or not

By doing below we can know --

1. function abc() {
 
}
if (typeof abc != 'undefined' && $.isFunction(abc)) {
    alert('abc exists');
} else {
    alert('abc does not exist');
}

if (typeof def  != 'undefined' && $.isFunction(def)) {
    alert('def exists');
} else {
    alert('def does not exist');
}

2. try {
            abc()
}
catch(e){alert("abc doesn't exist")}