w3resource

JavaScript: Swap the first and last elements of a given array of integers

JavaScript Basic: Exercise-80 with Solution

Write a JavaScript program to swap the first and last elements of a given array of integers. The array length should be at least 1.

Pictorial Presentation:

JavaScript: Swap the first and last elements of a given array of integers.

Sample Solution:

HTML Code:

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>JavaScript program to swap the first and last elements of a given array of integers. The array length should be  at least 1.</title>
</head>
<body>

</body>
</html>

JavaScript Code:

function swap(arra) {
    [arra[0], arra[arra.length - 1]] = [arra[arra.length - 1], arra[0]];
    return arra;
}
console.log(swap([1, 2, 3, 4]));  
console.log(swap([0, 2, 1]));  
console.log(swap([3])); 

Sample Output:

[4,2,3,1]
[1,2,0]
[3]

Flowchart:

Flowchart: JavaScript - Swap the first and last elements of a given array of integers

ES6 Version:

function swap(arra) {
    [arra[0], arra[arra.length - 1]] = [arra[arra.length - 1], arra[0]];
    return arra;
}
console.log(swap([1, 2, 3, 4]));  
console.log(swap([0, 2, 1]));  
console.log(swap([3])); 

Live Demo:

See the Pen JavaScript - swap the first and last elements of a given array of integers - basic-ex-80 by w3resource (@w3resource) on CodePen.


Contribute your code and comments through Disqus.

Previous: Write a JavaScript program to test if a given array of integers contains 30 and 40 twice.
Next: Write a JavaScript program to add two digits of a given positive integer of length two.

What is the difficulty level of this exercise?



JavaScript: Tips of the Day

Promise object

const myPromise = () => Promise.resolve('I have resolved!');

function firstFunction() {
  myPromise().then(res => console.log(res));
  console.log('second');
}

async function secondFunction() {
  console.log(await myPromise());
  console.log('second');
}

firstFunction();
secondFunction();

With a promise, we basically say I want to execute this function, but I'll put it aside for now while it's running since this might take a while. Only when a certain value is resolved (or rejected), and when the call stack is empty, I want to use this value.
We can get this value with both .then and the await keyword in an async function. Although we can get a promise's value with both .then and await, they work a bit differently.
In the firstFunction, we (sort of) put the myPromise function aside while it was running, but continued running the other code, which is console.log('second') in this case. Then, the function resolved with the string I have resolved, which then got logged after it saw that the callstack was empty.
With the await keyword in secondFunction, we literally pause the execution of an async function until the value has been resolved before moving to the next line.
This means that it waited for the myPromise to resolve with the value I have resolved, and only once that happened, we moved to the next line: second got logged.

Ref: https://bit.ly/3jFRBje