Javascript fucntion available or not

HTML

<input id="test" value="Available" onclick="ISfuctionAvailable();" type="button"/>

<input id="test1" value="Not available" onclick="fuctionNotAvailable();" type="button"/>

JavaScript

function ISfuctionAvailable(){
    if(typeof fuctionNotAvailable == 'function')
    {
        alert('Function available');
        //You can call function like  fuctionNotAvailable();
    }
    else
    {
        alert('Function Not available');
    }
}

function fuctionNotAvailable(){
    if(typeof test5 == 'function')
    {
        alert('Function available');
    }
    else
    {
        alert('Function Not available');
    }
}