exception.js

//add the given argument and throw exception object {name,message}
var add = function (a, b) {
    if (typeof a !== 'number' || typeof b !== 'number') {
             throw {
                 name: 'TypeError',
                 message: 'add needs numbers'
             }; 
    }
    return a + b; 
} 

//catch the exception
var try_it = function () { 
    try {
        add("seven");
    } catch (e) {
        document.writeln(e.name + ': ' + e.message);
    }
}

try_it( );