`1` ```exercism fetch javascript luhn ```

Luhn

Given a number determine whether or not it is valid per the Luhn formula.

The Luhn algorithm is a simple checksum formula used to validate a variety of identification numbers, such as credit card numbers and Canadian Social Insurance Numbers.

The task is to check if a given string is valid.

Validating a Number

Strings of length 1 or less are not valid. Spaces are allowed in the input, but they should be stripped before checking. All other non-digit characters are disallowed.

Example 1: valid credit card number

 `1` ```4539 1488 0343 6467 ```

The first step of the Luhn algorithm is to double every second digit, starting from the right. We will be doubling

 `1` ```4_3_ 1_8_ 0_4_ 6_6_ ```

If doubling the number results in a number greater than 9 then subtract 9 from the product. The results of our doubling:

 `1` ```8569 2478 0383 3437 ```

Then sum all of the digits:

 `1` ```8+5+6+9+2+4+7+8+0+3+8+3+3+4+3+7 = 80 ```

If the sum is evenly divisible by 10, then the number is valid. This number is valid!

Example 2: invalid credit card number

 `1` ```8273 1232 7352 0569 ```

Double the second digits, starting from the right

 `1` ```7253 2262 5312 0539 ```

Sum the digits

 `1` ```7+2+5+3+2+2+6+2+5+3+1+2+0+5+3+9 = 57 ```

57 is not evenly divisible by 10, so this number is not valid.

Setup

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

http://exercism.io/languages/javascript/installation

Making the Test Suite Pass

Execute the tests with:

 `1` ```jasmine .spec.js ```

Replace `<exercise-name>` with the name of the current exercise. E.g., to test the Hello World exercise:

 `1` ```jasmine hello-world.spec.js ```

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

Once you get a test passing, you can unskip the next one by changing `xit` to `it`.

Source

The Luhn Algorithm on Wikipedia http://en.wikipedia.org/wiki/Luhn_algorithm

Submitting Incomplete Solutions

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