List all the properties


#1

Why do the console display the values of all properties since I only set one property var?


#2

@frentea

T h e - B a s i c s

An object has one or more properties separated by a comma-,
Each property consists of a property-key and it's associated VALUE

var nyc = {
       fullName: "New York City",
       mayor: "Bill de Blasio",
       population: 8000000,
       boroughs: 5
      };
nyc -object- S p e c i f i e d

The nyc object has 4 properties separated by a comma-,
- a fullName property with property-key fullName and it's associated string value of "New York City"
- a mayor property with property-key mayor and it's associated string value of "Bill de Blasio"
- a population property with property-key population and it's associated number value 8000000
- a boroughs property with property-key boroughs and it's associated number value 5

for - in - loop - e x p l a i n e d

With the for-in-loop you have a Method
which will iterate over all properties of a given object.
At each iteration it will assign the property-key as a string
to a variable name of your choice.
Thus for (var x in nyc)
will lead to 4 iteration's
iteration-1 var x = "fullName";
iteration-2 var x = "mayor";
iteration-3 var x = "population";
iteration-4 var x = "boroughs";
As they want you to display the property-key and NOT it's associated VALUE
you would use
console.log( x );

If they wanted you to display the associated VALUE of the propery-key you would use
console.log( nyc[x] );


#3

So you are saying that "var a = "fullName" is unnecessary.
What if I just want to print out one value of the object property? How should I write the code?


#4

@frentea

= = = = = = = = = = = = = = = = = = = = = = = = = = = =

var james = {
    job: "programmer",
   married: false,
   sayJob: function() {
          // complete this method
          console.log("Hi, I work as a" + this.job);
    }
 };

Description of the james object.
The james object has 3 properties which are separated by a comma-,

there is a job property with property-key job and it's associated string value 'programmer'
there is a married property with property-key married and it's associated boolean value false
there is a sayJob property with property-key sayJob and it's associated anonymous function VALUE
( they also would 'say', the james-object has the sayJob()-Method )

access via dot-notation

(no variable allowed, only literal property-key-name )

james.job ==> you will get the associated string VALUE of the job property-key, thus
you get the string VALUE 'programmer'

james.married ==> you will get the associated boolean VALUE false

james.sayJob ==> you will get the associated anonymous function VALUE
to call/execute this method you add a pair of parenthesis-( )
james.sayJob();

access via the square-bracket-notation

1 using the literal property-key

james["job"]
james["married"]
james["sayJob"]()

2 using the property-key by reference (=== via a variable )

var propertyKey1 = "job";
var propertyKey2 = "married";
var propertyKey3 = "sayJob";
james[propertyKey1] ==> you will get the associated string VALUE of the job property-key, thus
you get the string "programmer"

james[propertyKey2]
in this case you will get the boolean VALUE of the married property
being false

james[propertyKey3]();
would =display= "Hi, I work as a programmer"

+++++++ this explanation +++++++++++
I defined an extra property in the james object.
in this case a method
as there is a property-key sayJob2
with it's associated value being a function...

var james = {
    job: "programmer",
    married: false,
    sayJob: function() {
              // no PARAMETER used
              // job-Value is picked up from within this Object
              console.log("Hi, I work as a" + " " + this.job);
    },
    sayJob2: function(job) {
              // 1 PARAMETER is used as =local= VARIABLE
              // job will get the  Value as you call providing 1 ARGUMENT
              console.log("Hi, I work as a" + " " + job);
    }
 
 };

 james.sayJob();

 james.sayJob2("xx");

An object has one or more properties separated by a comma-,
A property consists of a property-key and it's associated value.
The associated value can be anything
from an Array [] , null, "string", number, true , _an Object {} or a function.

If the associated value of a property-key is a function
we are calling this property a METHOD.
(if in the course they ask you to create a method you will now know that
you have to create a function within an object using the function-name
as property-key)

Normally if you are using the this keyword in a Method,
you are referring to the property of the object of which it is part of.

So in our case:
james.sayJob();
would translate to
console.log("Hi, I work as a" + " " + "programmer");

A good article about this:
http://stackoverflow.com/questions/80084/in-javascript-why-is-the-this-operator-inconsistent


#5

OK, Thanks! :slight_smile:


#6

@frentea

Please read the Function talk
and concentrate on
- parameter
- argument
- calling a function
- usage of the return statement

the FUNCTION talk

var myFunc = function( param1, param2) {
       //Begin of  anonymous FUNCTION-BODY
       //VARIABLE -myFunc- has an -anonymous function- assigned
       //this -anonymous function- has 2 PARAMETERS param1 and param2
       //param1 and param2 PARAMETERS are used 
       //as -local- VARIABLES throughout the FUNCTION-BODY

      console.log( param1 + " and " + param2 ) ;

      //End of anonymous FUNCTION-BODY
};

If you want to call/execute the anonymous function
you will have to add a pair of parentheses to the variable myFunc
like
myFunc();
As the anonymous function was defined
as having 2 parameters
you have to provide 2 arguments
in our case 2 string VALUES "Alena" and "Lauren"
like
myFunc("Alena","Lauren");

some quotes from the outer-world:

**argument is the value/variable/reference being passed in,
parameter is the receiving variable used within the function/block**

OR

**"parameters" are called "formal parameters",
while "arguments" are called "actual parameters".**

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

function with 1 parameter using return-statement

var myFunction = function( param1 ) {
       //Begin of FUNCTION-BODY
       //myFunction =function= has 1 PARAMETER param1
       //this param1 PARAMETER is used as a -local- VARIABLE
       //throughout the FUNCTION-BODY

      return param1;

      //End of FUNCTION-BODY
      };

you have defined a myFunction function
which takes 1 parameter param1
this param1 parameter is used
as a variable throughout the FUNCTION-BODY.

If you want to call/execute this myFunction function
and this myFunction function was defined
as having 1 parameter param1
you will have to provide 1 argument
in our case a "number VALUE" 4
myFunction( 4 );

some quotes from the outer-world:

**argument is the value/variable/reference being passed in,
parameter is the receiving variable used within the function/block**

OR

**"parameters" are called "formal parameters",
while "arguments" are called "actual parameters".**

============================================

As you are using the return-statement in your myFunction function
you will only get a return-value no-display.
You can however capture this return-value in a variable
and then use the console.log()-method to do a display.

var theResult = myFunction( 4 );
console.log( theResult );

OR directly

console.log( myFunction( 4 ) );

#7

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