Creating promises in Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new Promise that resolves with 'Done'.

Javascript

const promise = new Promise(([1]) => {
  resolve('Done');
});

Drag options to blanks, or click blank then click option'

Adone

Breject

Cresolve

Dcallback

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'reject' instead of 'resolve' when fulfilling the promise.

Using a parameter name that is not 'resolve' or 'reject'.

The Promise constructor takes a function with 'resolve' and 'reject' parameters. Here, we use 'resolve' to fulfill the promise.

2fill in blank

medium

Complete the code to create a Promise that rejects with an error message.

Javascript

const promise = new Promise((resolve, [1]) => {
  [1]('Error occurred');
});

Drag options to blanks, or click blank then click option'

Areject

Bresolve

Cfail

Derror

Attempts:

3 left

💡 Hint

Common Mistakes

Calling 'resolve' instead of 'reject' to reject the promise.

Using incorrect parameter names.

The second parameter of the Promise executor function is 'reject', used to reject the promise with an error.

3fill in blank

hard

Fix the error in the Promise executor function parameter to correctly create a Promise.

Javascript

const promise = new Promise([1] => {
  resolve('Success');
});

Drag options to blanks, or click blank then click option'

Aresolve

B()

C(callback)

D(resolve, reject)

Attempts:

3 left

💡 Hint

Common Mistakes

Using a single parameter without parentheses.

Omitting the reject parameter.

The Promise executor function must have two parameters: resolve and reject, enclosed in parentheses.

4fill in blank

hard

Fill both blanks to create a Promise that resolves after 1 second with 'Done'.

Javascript

const promise = new Promise(([1], [2]) => {
  setTimeout(() => [1]('Done'), 1000);
});

Drag options to blanks, or click blank then click option'

Aresolve

Breject

Ccallback

Ddone

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect parameter names.

Calling reject instead of resolve inside setTimeout.

The Promise executor function takes 'resolve' and 'reject'. We call 'resolve' inside setTimeout to fulfill the promise after 1 second.

5fill in blank

hard

Fill all three blanks to create a Promise that resolves with the uppercase version of input after 500ms.

Javascript

function toUpperAsync(str) {
  return new Promise(([1], [2]) => {
    setTimeout(() => [1](str[3]), 500);
  });
}

Drag options to blanks, or click blank then click option'

Aresolve

Breject

C.toUpperCase()

D.toLowerCase()

Attempts:

3 left

💡 Hint

Common Mistakes

Using .toLowerCase() instead of .toUpperCase().

Calling reject instead of resolve.

Missing parentheses around parameters.

The Promise executor uses 'resolve' and 'reject'. We call resolve with str.toUpperCase() after 500ms.