JavaScript by reference vs. by value [duplicate]

Answer 1

1. Primitive type variable like string,number are always pass as pass by value.

2. Array and Object is passed as pass by reference or pass by value based on these two condition.

   • if you are changing value of that Object or array with new Object or Array then it is pass by Value.

     object1 = {item: "car"}; array1=[1,2,3];

   here you are assigning new object or array to old one.you are not changing the value of property of old object.so it is pass by value.

   • if you are changing a property value of an object or array then it is pass by Reference.

     object1.item= "car"; array1[0]=9;

   here you are changing a property value of old object.you are not assigning new object or array to old one.so it is pass by reference.

Code

    function passVar(object1, object2, number1) {

        object1.key1= "laptop";
        object2 = {
            key2: "computer"
        };
        number1 = number1 + 1;
    }

    var object1 = {
        key1: "car"
    };
    var object2 = {
        key2: "bike"
    };
    var number1 = 10;

    passVar(object1, object2, number1);
    console.log(object1.key1);
    console.log(object2.key2);
    console.log(number1);

Output: -
    laptop
    bike
    10