 # JavaScript: Compute the sum of two parts and store into an array of size two

## JavaScript Basic: Exercise-85 with Solution

Write a JavaScript code to divide a given array of positive integers into two parts. First element goes to first part, second element goes to second part, and third element goes to first part and so on. Now compute the sum of two parts and store into an array of size two.

Pictorial Presentation: Sample Solution:

HTML Code:

``````<!DOCTYPE html>
<html>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width">
<title>Compute the sum of two parts and store into an array of size two</title>
<body>

</body>
</html>
```
```

JavaScript Code:

``````function alternate_Sums(arr) {
var result = [0, 0];
for(var i = 0; i < arr.length; i++)
{
if(i % 2) result += arr[i];
else
result += arr[i];
}
return result
}

console.log(alternate_Sums([1, 3, 6, 2, 5, 10]))
```
```

Sample Output:

```[12,15]
```

Flowchart: ES6 Version:

``````function alternate_Sums(arr) {
const result = [0, 0];
for(let i = 0; i < arr.length; i++)
{
if(i % 2) result += arr[i];
else
result += arr[i];
}
return result
}

console.log(alternate_Sums([1, 3, 6, 2, 5, 10]))
``````

Live Demo:

See the Pen javascript-basic-exercise-85 by w3resource (@w3resource) on CodePen.

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