Test Your JavaScript Skills : ES12 (JavaScript 2021) - 39

Introduction

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

1. Identify the output of the below program

    let p1 = Promise.reject("Error 1");
    let p2 = Promise.reject("Error 2");
   
    Promise.any([p1,p2])
      .then((value) => {
        console.log(value); 
      })
   

   a.Error 1

   b.Error 2

   c.Crash

   d.No output

   e.Error 1 Error 2

   Answer:c

   Reason:The above code does not handle an error situation hence crashes.

2. Identify the output of the below program

   
    let pr = new Promise((resolve, reject) => {
        reject("fails");
      });
   
      let pr2 = new Promise((resolve, reject) => {
        setTimeout(reject, 500, "Completed");
      });
   
      let pr3 = new Promise((resolve, reject) => {
        setTimeout(reject, 100, "Fast");
      });
   
      Promise.any([pr, pr2, pr3]).then((value) => {
        console.log(value); 
      });
   

   a.fails

   b.Completed

   c.Fast

   d.Crash

   e.No output

   Answer:d

   Reason:All the promises are rejected and are also not handled hence application crashes.

3. Identify the output of the below program

    class Emp {
        eno;
        ename;
        constructor(eno, ename) {
            this.eno = eno;
            this.ename = ename;
        }
        show() {
            console.log(this.eno, this.ename);
        }
        #update(eno, ename) {
            this.eno = eno;
            this.ename = ename;
        }
    };
   
    let obj = new Emp(1, "Ram");
    obj.update(2,"Gopi");
   

   a.error

   b.1 Ram

   c.2 Gopi

   d.no output

   e.undefined

   Answer:a

   Reason:The private method cannot be accessed on an object.

4. Identify the output of the below program

    let abc="ram"
    let ref = new WeakRef(abc); 
    let wkref = ref.deref();
    console.log(wkref);
   

   a.ram

   b.undefined

   c.error

   d.Object

   e.null

   Answer:c

   Reason:Cannot create a weak reference for string.

5. Identify the output of the below program

   
    let p1 = Promise.reject("Error 1");
    let p2 = Promise.reject("Error 2");
    let p3 = Promise.resolve("Success");
   
    Promise.any([p1, p2, p3])
      .then((value) => {
        console.log(value); 
      })
      .catch((error) => {
        console.log(error); 
      });
   

   a.Error 1

   b.Error 2

   c.Success

   d.AggregateError

   e.No output

   Answer:c

   Reason:The first completed promise is handled by Promise.any() function.

6. Identify the output of the below program

    let abc= () => {}
    let ref = new WeakRef(abc); 
    let wkref = ref.deref();
    console.log(wkref);
   

   a.error

   b.function

   c.Object

   d.undefined

   e.()=>{}

   Answer:e

   Reason:Function is an object hence weak reference can be created.

7. Identify the output of the below program

   
    let pr = new Promise((resolve, reject) => {
        reject("fails");
      });
   
      let pr2 = new Promise((resolve, reject) => {
        setTimeout(resolve, 500, "Completed");
      });
   
      let pr3 = new Promise((resolve, reject) => {
        setTimeout(resolve, 100, "Fast");
      });
   
      Promise.any([pr, pr2, pr3]).then((value) => {
        console.log(value); 
      });
   

   a.fails

   b.Completed

   c.Fast

   d.Error

   e.No output

   Answer:c

   Reason:The first completed promise is handled by Promise.any() function.

8. Identify the output of the below program

    class Emp {
        eno;
        ename;
        constructor(eno, ename) {
            this.eno = eno;
            this.ename = ename;
        }
        #show() {
            console.log(this.eno, this.ename);
        }
        update(eno, ename) {
            this.eno = eno;
            this.ename = ename;
            this.#show();
        }
    };
   
    let obj = new Emp(1, "Ram");
    obj.update(2,"Gopi");
   

   a.1 Ram

   b.2 Gopi

   c.error

   d.undefined

   e.no output

   Answer:b

   Reason:The update() function calls the private function show().

9. Identify the output of the below program

    let student = {
        name: 'Ram',
        age: 20,    
      };
   
    let ref = new WeakRef(student); 
    let wkref = ref.deref();
    console.log(wkref.name);
   

   a.Ram

   b.Error

   c.undefined

   d.20

   e.garbage value

   Answer:a

   Reason:The original object is still alive hence de-referencing works.

10. Identify the output of the below program

    ```javascript

    let p1 = Promise.reject("Error 1"); let p2 = Promise.reject("Error 2");

Promise.any([p1, p2]) .then((value) => { console.log(value); }) .catch((error) => { console.log(error); }); ```

a.Error 1

b.Error 2

c.AggregateError

d.No output

e.undefined

Answer:c

Reason:When all promises are rejected the catch is called which prints AggregateError.