add_property_to_an_object.js

// Description:
// Write a function that adds a named property to an object. It must be possible to set the property to a new value. If the property already exists on the object, and error should be thrown.

// SOLUTION:

function addProperty(obj, prop, value) {
    if (prop in obj) {
        throw new Error('Error message');

    } else {
        obj[prop] = value;

    }
}