Published at Aug 25 2018
·
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Instructions

Test suite

Solution

An Armstrong number is a number that is the sum of its own digits each raised to the power of the number of digits.

For example:

- 9 is an Armstrong number, because
`9 = 9^1 = 9`

- 10 is
*not*an Armstrong number, because`10 != 1^2 + 0^2 = 2`

- 153 is an Armstrong number, because:
`153 = 1^3 + 5^3 + 3^3 = 1 + 125 + 27 = 153`

- 154 is
*not*an Armstrong number, because:`154 != 1^3 + 5^3 + 4^3 = 1 + 125 + 64 = 190`

Write some code to determine whether a number is an Armstrong number.

Go through the setup instructions for ECMAScript to install the necessary dependencies:

http://exercism.io/languages/ecmascript

Install assignment dependencies:

```
$ npm install
```

Execute the tests with:

```
$ npm test
```

In the test suites all tests but the first have been skipped.

Once you get a test passing, you can enable the next one by
changing `xtest`

to `test`

.

Wikipedia Narcissistic number

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

```
import { validate } from './armstrong-numbers';
describe('ArmstrongNumber', () => {
test('Single digit numbers are Armstrong numbers', () => {
const input = 5;
expect(validate(input)).toBe(true);
});
xtest('There are no 2 digit Armstrong numbers', () => {
const input = 10;
expect(validate(input)).toBe(false);
});
xtest('Three digit number that is an Armstrong number', () => {
const input = 153;
expect(validate(input)).toBe(true);
});
xtest('Three digit number that is not an Armstrong number', () => {
const input = 100;
expect(validate(input)).toBe(false);
});
xtest('Four digit number that is an Armstrong number', () => {
const input = 9474;
expect(validate(input)).toBe(true);
});
xtest('Four digit number that is not an Armstrong number', () => {
const input = 9475;
expect(validate(input)).toBe(false);
});
xtest('Seven digit number that is an Armstrong number', () => {
const input = 9926315;
expect(validate(input)).toBe(true);
});
xtest('Seven digit number that is not an Armstrong number', () => {
const input = 9926314;
expect(validate(input)).toBe(false);
});
});
```

```
function validate(input) {
let numArr = input.toString().split('');
return numArr.reduce((sum,x)=>sum+=Number(x)**numArr.length,0)===input;
}
module.exports={validate};
```

A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

- What compromises have been made?
- Are there new concepts here that you could read more about to improve your understanding?

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