Test Your JavaScript Skills : ES11 (JavaScript 2020) - 40

Introduction

Namaste, In this blog I will discuss 10 code scenarios on Javascript .

1. Identify the output of the below program

    let obj = {
        name: {
            firstname : "ram",
            lastname : "kumar"
        }
    }
    console.log(obj.name.middlename.name);
   

   a.undefined

   b.null

   c.crash

   d.kumar

   e.ram

   Answer:c

   Reason:It crashes because middlename.name does not exist on obj.name.

2. Identify the output of the below program

    let arr =null;
    console.log(arr[1]);
   

   a.null

   b.undefined

   c.crash

   d.1

   e.0

   Answer:c

   Reason:The program crashes because arr is initialized to null.

3. Identify the output of the below program

    let fx = () => console.log("fx");
    fx = null;
    fx?.();
   

   a.null

   b.fx

   c.undefined

   d.no output

   e.crash

   Answer:d

   Reason: Since fx is initialized to null the function is not called (but does not crash).

4. Identify the output of the below program

    let num = null
     num = num ?? 5
    console.log(num)
   

   a.null

   b.undefined

   c.error

   d.5

   e.no output

   Answer:d

   Reason:Nullish operator returns 5 as the num is null.

5. Identify the output of the below program

    const big = 1234124123412412341234123412341234n;
    console.log(typeof big);
   

   a.int

   b.number

   c.float

   d.error

   e.bigint

   Answer:e

   Reason:A integer value suffixed by n is bigint type.

6. Identify the output of the below program

    let big = BigInt(45252345235252352353523534523453252345235235345);
    console.log(typeof big);
   

   a.number

   b.int

   c.bigint

   d.error

   e.float

   Answer:c

   Reason:A variable assigned by function BigInt is bigint type.

7. Identify the output of the below program

    let obj = {
        name: {
            firstname : "ram",
            lastname : "kumar"
        }
    }
    console.log(obj.name.middlename?.name);
   

   a.null

   b.ram

   c.crash

   d.undefined

   e.kumar

   Answer:d

   Reason:The optional chaining operator returns undefined for non existent properties.

8. Identify the output of the below program

    let arr =null;
    console.log(arr?.[1]);
   

   a.null

   b.undefined

   c.1

   d.crash

   e.no output

   Answer:b

   Reason:For non existent index access the optional chaining operator returns undefined.

9. Identify the output of the below program

   
    let obj = {
        name: {
            firstname : "ram",
            lastname : "kumar"
        }
    }
   
    console.log(obj.name.middlename?.name ?? "Default");
   

   a.undefined

   b.null

   c.error

   d.ram

   e.Default

   Answer:e

   Reason:By computation the value displayed is Default.

10. Identify the output of the below program

    let obj = {
        name: {
            firstname : "ram",
            lastname : "kumar"
        }
    }
    console.log(obj.name.middlename ?? "default");
    

    a.ram

    b.kumar

    c.undefined

    d.default

    e.error

    Answer:d

    Reason:Since middlename property is non existent default is printed.