Understanding javascript objects

JavaScript
1

From the freecodecamp video i am trying to follow on youtube i am trying
to understand why its [checkProp] instead of .checkProp i thought
that with objects it was dot annotation or with {} if the strings have spaces
in beyween

var myObj = {

‘gift’: ‘pony’,

‘pet’: ‘kitten’,

‘bed’: ‘sleigh’

};

function checkObj(checkProp) {

if(myObj.hasOwnProperty(checkProp)) {

**return myObj[checkProp]** ; 

 } else {

   return 'none';

 }

}

console.log(checkObj(‘bed’));

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2

Here you are able to pass in a variable as the object key instead of specifying in code the key name obj.keyname ← cannot change

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3

in this case doesn’t checkProp represent the property name within the object myObj? i.e gift.

4

Dot notation try to access literally a property of that name, bracket notation will evaluate what’s inside the brackets before accessing the property

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5

Here’s an easy way to understand it.

dot notation requires the property to match literally.

example

let car = {
“first”: “mustang”
};

console.log(car.first); // mustang
console.log(car["first"]); // mustang

That’s because “first” matches the key literally inside of the car object.

Now say you did this:

let car = {
    "first":    "mustang"
};
let variable = "first";

console.log(car.variable); // undefined
console.log(car[variable]); // mustang

That’s because .variable is not a key inside of car. So you must use the square bracket to get the value of variable rather than the literal string variable.

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6

in this case doesn’t checkProp represent the property name within the object myObj? i.e gift.

Yes, correct. checkProp is the variable inside the scope of the function

7

ok, i am slightly confused in my example shouldn’t it be literal matching as
the property we are trying to call is within the object?

8

Why would it be literally checking when you’re using square brackets? Did you read my post thoroughly?

return myObj[checkProp] ;

9

This object has a property with a key ‘gift’
This object has a property with a key ‘pet’
This object has a property with a key ‘bad’

var myObj = {
 gift: ‘pony’,
 pet: ‘kitten’,
 bed: ‘sleigh’
};

This object does not have a property with a key ‘checkProp’

10

ok i think i have understood, it has to be an exact checkProp is an argument that
represents the property but not the exact property which is why myObj[checkProp]
is required.