Layman's explanation:
An object is a collection of properties. You can give a name to the object to keep things organized. For example, lets create a person object.
var person = {};
The object has no properties right now. To further describe the person we can add properties to the object.
person.Name = 'Zim';
person.Age = 29;
person.Gender = 'Male';
person.Weight = 80;
Now this object has some properties to help describe it. A different way to write the same thing:
var person = { Name: 'Zim', Age: 29, Gender: 'Male', Weight: 80 };
If we had to create a program that displays a list of people, storing all of our information inside objects would help keep things organized.
Object properties are sometimes referred to as keys.
Adding properties to objects:
You can add a property to an object using brackets, just like you had in your addProperty function. If you just need it to add a property, set that property to null and return the result it would look something like this:
function addProperty(object, property) {
// code here
object[property] = null;
return object;
}
This would let us create a properies on our object from above by calling
addProperty(person, 'Occupation');
addProperty(person, 'Income');
addProperty(person, 'Height');
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Layman's explanation:
An object is a collection of properties. You can give a name to the object to keep things organized. For example, lets create a person object.
var person = {};
The object has no properties right now. To further describe the person we can add properties to the object.
person.Name = 'Zim';
person.Age = 29;
person.Gender = 'Male';
person.Weight = 80;
Now this object has some properties to help describe it. A different way to write the same thing:
var person = { Name: 'Zim', Age: 29, Gender: 'Male', Weight: 80 };
If we had to create a program that displays a list of people, storing all of our information inside objects would help keep things organized.
Object properties are sometimes referred to as keys.
Adding properties to objects:
You can add a property to an object using brackets, just like you had in your addProperty function. If you just need it to add a property, set that property to null and return the result it would look something like this:
function addProperty(object, property) {
// code here
object[property] = null;
return object;
}
This would let us create a properies on our object from above by calling
addProperty(person, 'Occupation');
addProperty(person, 'Income');
addProperty(person, 'Height');
I think you're over-thinking it.
First the question:
Add the value of the property argument as a key on the object argument. The value of the new property should be set to null. Return object after adding the new property.
emphasis added
So, property will be the KEY (of a key/value pair), and the VALUE will be null of object, which we are also passing in as an argument.
One way to interrogate key/value pairs on a javascript object is through the square-brackets []. So, if you have a key/value pair: { foo: "bar" }, you can get "bar" by: object['foo']. You can also create new key/value pairs like this, so your function can look like:
function addProperty(object, property) {
object[property] = null;
return object;
}
var obj = {};
obj = addProperty(obj, "hello");
console.log(obj);
console.log(addProperty({x: 5}, 'y'));
What our function is doing is taking the object passed into it (as an argument), creating a new KEY with our property argument, and setting its VALUE to null, and simply returning the object.
*Side note -
Be careful, the code you have posted will create an endless recursive loop, as you keep calling the same function with no way to break out of it.
In modern browsers (IE9+, FF4+, Chrome5+, Opera12+, Safari5+) you can use the built in Object.keys method:
var keys = Object.keys(myObject);
The above has a full polyfill but a simplified version is:
var getKeys = function(obj){
var keys = [];
for(var key in obj){
keys.push(key);
}
return keys;
}
Alternatively replace var getKeys with Object.prototype.keys to allow you to call .keys() on any object. Extending the prototype has some side effects and I wouldn't recommend doing it.
As slashnick pointed out, you can use the "for in" construct to iterate over an object for its attribute names. However you'll be iterating over all attribute names in the object's prototype chain. If you want to iterate only over the object's own attributes, you can make use of the Object#hasOwnProperty() method. Thus having the following.
for (var key in obj) {
if (obj.hasOwnProperty(key)) {
/* useful code here */
}
}