+ 2

Value vs Reference

function changeAgeAndReference(person) { person.age = 25; person = { name: 'John', age: 50 }; return person; } var personObj1 = { name: 'Alex', age: 30 }; var personObj2 = changeAgeAndReference(personObj1); console.log(personObj1); // -> { name: 'Alex', age: 25 } console.log(personObj2); // -> { name: 'John', age: 50 } why doesn't person(John, 50) in the first function overwrite person in the centre(Alex, 30)

2nd Jun 2018, 1:17 PM
IZzZI
IZzZI - avatar
7 Antworten
+ 1
Because although you send Alex/30, you override that inside the function to John/50... I am wonderibg how you get Alex/25 when you don't call that function...
2nd Jun 2018, 1:33 PM
Jiří Bočan
+ 1
person is a parameter that first refers to person1, but then you change the reference to person2, but this only affects the parameter not the object
2nd Jun 2018, 3:17 PM
Dan Walker
Dan Walker - avatar
+ 1
IZzZI sorry didn't mean personObj2, I meant the reference changes to another person object throughout the function. That is, when the first line (person.x = 25) is executed, person does indeed refer to personObj1, but in the next line the parameter 'person' is given a new object. We lose our *reference* to personObj1 and start modifying a new entity, which is then returned.
2nd Jun 2018, 3:40 PM
Dan Walker
Dan Walker - avatar
0
Jiří Bočan Can you elaborate your answer please. Thank You. Btw the function is called when var personObj2 = changeAgeAndReference(personObj1);
2nd Jun 2018, 1:40 PM
IZzZI
IZzZI - avatar
0
Check this: function changeAgeAndReference(person) { person.age = 25; person = { name: 'John', age: 50 }; return person; } var personObj1 = { name: 'Alex', age: 30 }; console.log(personObj1); // -> { name: 'Alex', age: 30 } var personObj2 = changeAgeAndReference(personObj1); console.log(personObj1); // -> { name: 'Alex', age: 25 } console.log(personObj2); // -> { name: 'John', age: 50 } ` ------- The first console.log() shows you the original personObj1 (Alex/30). The second console.log() gives Alex/25 because you change the age value of "person" = "personObj1", which is a function argument, by assigning "person.age = 25;". And then, regardless of what the "person" argument is like, you override/redefine the "person" object completely - you override both name and age by person = { name: 'John', age: 50 }; (this is what changeAgeAndReference() returns: John/50).
2nd Jun 2018, 2:20 PM
Jiří Bočan
0
I understand everything except this. After the function is called person = personObj1 right? var personObj1 = { name: 'Alex', age: 30 }; person = { // person = personObj1 name: 'John', age: 50 }; Since both objects are referring to personObj1, shouldn't the second object override the first one?
2nd Jun 2018, 2:39 PM
IZzZI
IZzZI - avatar
0
Dan Walker when did i change my reference to personObj2?
2nd Jun 2018, 3:24 PM
IZzZI
IZzZI - avatar