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The-Algorithms-JavaScript/String/ValidateCreditCard.js at master · foo123/The-Algorithms-JavaScript · GitHub
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The-Algorithms-JavaScript
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String
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ValidateCreditCard.js
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ValidateCreditCard.js
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/**
* Validate a given credit card number
*
* The core of the validation of credit card numbers is the Luhn algorithm.
*
* The validation sum should be completely divisible by 10 which is calculated as follows,
* every first digit is added directly to the validation sum.
* For every second digit in the credit card number, the digit is multiplied by 2.
* If the product is greater than 10 the digits of the product are added.
* This resultant digit is considered for the validation sum rather than the digit itself.
*
* Ref: https://www.geeksforgeeks.org/luhn-algorithm/
*/
const
luhnValidation
=
(
creditCardNumber
)
=>
{
let
validationSum
=
0
creditCardNumber
.
split
(
''
)
.
forEach
(
(
digit
,
index
)
=>
{
let
currentDigit
=
parseInt
(
digit
)
if
(
index
%
2
===
0
)
{
// Multiply every 2nd digit from the left by 2
currentDigit
*=
2
// if product is greater than 10 add the individual digits of the product to get a single digit
if
(
currentDigit
>
9
)
{
currentDigit
%=
10
currentDigit
+=
1
}
}
validationSum
+=
currentDigit
}
)
return
validationSum
%
10
===
0
}
const
validateCreditCard
=
(
creditCardString
)
=>
{
const
validStartSubString
=
[
'4'
,
'5'
,
'6'
,
'37'
,
'34'
,
'35'
]
// Valid credit card numbers start with these numbers
if
(
typeof
creditCardString
!==
'string'
)
{
throw
new
TypeError
(
'The given value is not a string'
)
}
const
errorMessage
=
`
${
creditCardString
}
is an invalid credit card number because `
if
(
isNaN
(
creditCardString
)
)
{
throw
new
TypeError
(
errorMessage
+
'it has nonnumerical characters.'
)
}
const
creditCardStringLength
=
creditCardString
.
length
if
(
!
(
creditCardStringLength
>=
13
&&
creditCardStringLength
<=
16
)
)
{
throw
new
Error
(
errorMessage
+
'of its length.'
)
}
if
(
!
validStartSubString
.
some
(
(
subString
)
=>
creditCardString
.
startsWith
(
subString
)
)
)
{
throw
new
Error
(
errorMessage
+
'of its first two digits.'
)
}
if
(
!
luhnValidation
(
creditCardString
)
)
{
throw
new
Error
(
errorMessage
+
'it fails the Luhn check.'
)
}
return
true
}
export
{
validateCreditCard
}
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