JavaScript Promises with setTimeout Examples

Promise with setTimeout:

Write a JavaScript function that creates a Promise that resolves after a given number of milliseconds.

Solution-1: Using a Named Function

Code:

// Function to create a promise that resolves after a given number of milliseconds
function delay(milliseconds) {
  // Return a new promise
  return new Promise((resolve) => {
    // Use setTimeout to delay execution
    setTimeout(() => {
      resolve(`Resolved after ${milliseconds} milliseconds`);
    }, milliseconds);
  });
}

// Test the function
delay(2000).then((message) => console.log(message)); // Logs: Resolved after 2000 milliseconds

Output:

"Resolved after 2000 milliseconds"

Explanation:

• The delay function takes milliseconds as an argument.
• It returns a new Promise.
• Inside the promise, setTimeout delays execution for the specified milliseconds.
• After the delay, the promise resolves with a message indicating the delay duration.
• The .then() method logs the resolved message when the promise resolves.

Solution-2: Using an Arrow Function

Code:

// Arrow function to create a promise that resolves after a given time
const delay = (milliseconds) =>
  new Promise((resolve) => {
    // Use setTimeout for the delay
    setTimeout(() => resolve(`Done waiting ${milliseconds} ms`), milliseconds);
  });

// Test the function
delay(3000).then((message) => console.log(message)); // Logs: Done waiting 3000 ms

Output:

"Done waiting 3000 ms"

Explanation:

• The delay function is written as an arrow function.
• It takes milliseconds as input and returns a new Promise.
• Inside the promise, setTimeout is used to wait for the specified time before resolving.
• The message includes the delay time and is logged when the promise resolves.

See the Pen promises-and-async-await-exercise-11 by w3resource (@w3resource) on CodePen.

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