JavaScript-Concepts/reference_vs_value.html at master · kipchirchiralb/JavaScript-Concepts · GitHub

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<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <style>
        .wrapper {
            margin: 0 auto;
            text-align: center;
        }
    </style>
    <title>Reference vs Value</title>
</head>

<body>
    <div class="wrapper">
        <h1>Pass by value and pass by Reference</h1>

    </div>
    <script>
        /*
                                                //********************PART 1****
                                                // pass by value / setting by value - taking anything that is on the right hand side of the equal sign and copie its value to the variable on the left hand side of the equals sign.

                                                let a = 10
                                                let b = "Hi"
                                                let c = a
                                                console.log(a)
                                                console.log(b)
                                                console.log(c)

                                                c = c + 1

                                                console.log(c)

                                                //Anything tha is not a primitive type (boolean , string , integer) is passed by reference. These include objects such as arrays and objects
                                                // a reference(a memory address) to that object or array is stored in the value of the variable
                                                c = [1, 2]
                                                console.log(c)
                                                let d = c // takes value of c and copies to d which are references to memory. these two will point to the same adrress.
                                                console.log(d)
                                                d.push(3) //will change both c and d since they both point to the same address. THIS IS WHERE WE MIGHT RUN INTO BUGS/ ERRORS
                                                console.log(d) //[1,2,3]
                                                console.log(c) //[1,2,3]

                                                d = [3, 4, 5] //Another pointer to a new place in memory that is holding the array [3,4,5]. This overrides the value of d but c remains the same.
                                                console.log(d)
                                                console.log(c) // [1,2,3]
                                                d.push(6)
                                                d.push(7)
                                                console.log(d)
                                                console.log(c)

                                                //practical difference

                                                let x = [1, 2]
                                                let y = x // y is getting x by value , this value is the reference to the array [1,2]
                                                console.log(x === y) //true
                                                console.log(x == y) //true

                                                y = [1,2] // y is getting its own memory address / references which is different from x's .
                                                console.log(x === y) //false - since we are comparing two different references to locations in memory
                                                console.log(x == y) //false - same case
                                                */


        //*********PART 2**
        let c = [1, 2]
        add(c, 3)

        function add(array, element) {
            array.push(element)
        }
        console.log(c)

        //PRIMITIVE VALUES such as numbers, strings, boolean, undefined, null are passed by values

        // arrays, objects , classes etc are passed by reference.They can be modified without changing their memory location
        //e.g
        const k = [1, 2, 3]
        k.push(15) //we can modify the values in the array but not the location/ refernence in memory
        console.log(k)
    </script>
</body>

</html>