How to handle Regex returned as string?

Question

Kindly note, I tried some suggestions from other SO post about regexp, none helped!!! Coming to the question -

I have JSON data like this (original: https://api.myjson.com/bins/fvzpp):

{
  VISA: {
    cardPattern: "/^4/",
    cardNumberLength: 16,
    cvv: "required",
    cvvLength: 3,
    displayText: "Visa"
  },
  MASTERCARD: {
    cardPattern: "/^5[1-5]/",
    cardNumberLength: 16,
    cvv: "required",
    cvvLength: 3,
    displayText: "Master"
  },
  MAESTRO: {
    cardPattern:
      "/^(50|63|66|5[6-8]|6[8-9]|600[0-9]|6010|601[2-9]|60[2-9]|61|620|621|6220|6221[0-1])/",
    cardNumberLength: 19,
    cvv: "optional",
    cvvLength: 4,
    displayText: "Maestro"
  }
}

Please see the cardPattern property which is in string format. How do i make use of the same to test a string(say 445). For example, "/^4/".test(mysttring) does not work. And also var reg = new RegExp("/^4/") returns a weird //^4// which will never match mystring. How to handle such a response for regex? Just to be more explicit, how to handle response['VISA'].cardPattern.test(4545) which should have worked, but does not!

And also, The response is not JSON format, and is object inside object. What is the best way to parse such a response? I tried for-in loop, but that returns 'VISA', 'MASTERCARD' and 'MAESTRO'(the strings) which is not what I want.

@AdarshMohan - That's not the point. How to handle from the call example - response['VISA'].cardPattern.test(4545)? It should have worked, but will not!!! — ramesh en
– ramesh en, Commented Oct 8, 2017 at 16:00
remove the leading and trailing slashes and then passing as an argument to RegExp like.. new RegExp(response.VISA.cardPettern.replace(“/“,””).replace(/\/$/,””)).test(4545); maybe you can combine the two replace with a single regex — Adarsh Mohan
– Adarsh Mohan, Commented Oct 8, 2017 at 16:05

AKX · Accepted Answer · 2017-10-08 16:08:08Z

2

You'll have to use the new RegExp() constructor to parse the regexp first.

However, you'll have to strip the leading and trailing slashes:

function parseCardPattern(cardPattern) {
  return new RegExp(cardPattern.substr(1, cardPattern.length - 2));
}

You can now use the regexp object for testing:

const visaPattern = parseCardPattern(response['VISA'].cardPattern);
console.log(visaPattern.test('4242424242'));  // => True

answered Oct 8, 2017 at 16:08

AKX

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A l w a y s S u n n y · Accepted Answer · 2017-10-08 16:05:39Z

If I don't misunderstood your question. Grab cardPattern like this json.VISA.cardPattern and then try like this

let json = {"VISA":{"cardPattern":"/^4/","cardNumberLength":16,"cvv":"required","cvvLength":3,"displayText":"Visa"},"MASTERCARD":{"cardPattern":"/^5[1-5]/","cardNumberLength":16,"cvv":"required","cvvLength":3,"displayText":"Master"},"MAESTRO":{"cardPattern":"/^(50|63|66|5[6-8]|6[8-9]|600[0-9]|6010|601[2-9]|60[2-9]|61|620|621|6220|6221[0-1])/","cardNumberLength":19,"cvv":"optional","cvvLength":4,"displayText":"Maestro"}};
const regex = json.VISA.cardPattern;
const str = `4545`;
let m;

while ((m = regex.exec(str)) !== null) {
    // This is necessary to avoid infinite loops with zero-width matches
    if (m.index === regex.lastIndex) {
        regex.lastIndex++;
    }

    // The result can be accessed through the `m`-variable.
    m.forEach((match, groupIndex) => {
        console.log(`Found match, group ${groupIndex}: ${match}`);
    });
}

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