How to use a function on each array within an array

Question

I'm trying to run a function on each array within an array, however it only seems to run the iteration once, i dont get any error messages to help me figure out why?

its a basic credit card checker project

// An array of all the arrays above
const batch = [valid1, valid2, valid3, valid4, valid5, invalid1, invalid2, invalid3, invalid4, invalid5, mystery1, mystery2, mystery3, mystery4, mystery5];


// Add your functions below:
const validateCred = (arr) =>{
  let totalSum = 0
  let newArr = arr.slice(0);
  let lastDigit = newArr.pop()
  newArr = newArr.reverse()
  for(i = 0; i < newArr.length; i++){
    if (i % 2 === 0){
      let doubled = newArr[i] * 2
      if (doubled > 9){
        doubled -= 9
      }
      totalSum += doubled
    } else {
      totalSum += newArr[i]
    }
  }

  if((totalSum + lastDigit) % 10 === 0){
    return true
  } else {
    return false
  }
};

const findInvalidCards = (arrBatch) =>{
  let invalidCred = []
  for(i = 0; i<arrBatch.length; i++){
    console.log(validateCred(arrBatch[i]))
  }
};

findInvalidCards(batch);```

Please post the the proper input example for batch. It will help to debug faster — Sunil Chaudhary
– Sunil Chaudhary, Commented Dec 10, 2019 at 22:13

Marwan · Accepted Answer · 2019-12-10 22:18:38Z

1

You are declaring i as a global variable in both for-loops. That could be the problem.

Try replacing for(i = 0; with for(let i = 0; both in validateCred and findInvalidCards

answered Dec 10, 2019 at 22:18

Marwan

1561 silver badge4 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Jperkins98 Over a year ago

This worked perfectly, could you explain a little as to how it was causing it to exit after one run, just so i can get my head around it.

patstuart · Accepted Answer · 2019-12-10 22:17:34Z

1

The problem is that i is not a local variable. The inner function updates i in the global scope, so the outer function exits after only one run.

Change for (i = 0... to for (var i = 0 and it should run.

answered Dec 10, 2019 at 22:17

patstuart

1,9901 gold badge20 silver badges30 bronze badges

2 Comments

Jperkins98 Over a year ago

This worked perfectly, could you explain a little as to how it was causing it to exit after one run, just so i can get my head around it.

patstuart Over a year ago

@Jperkins98 In Javascript, if you use const, let, or var, it creates a variable which can only be accessed by that function or any functions in "scope." If you forget to declare the variable, Javascript will automatically create the variable and assign it to the global (i.e., window) context. This means validateCred is changing the global value of i to 8. When findInvalidCards runs checks the loop condition i<arrBatch.length, it evaluates to true after the first run. You can read more here: w3schools.com/js/js_scope.asp.

Bibberty · Accepted Answer · 2019-12-10 22:17:43Z

0

A simple filter will work.

Looks like you are doing a Luhn check on each number, should be easy to transpose that code onto this model.

const sampleArray = [0,1,2,0,6,0,4,5,8];

const validNum = (num) => num > 0;

const validNumbers = sampleArray.filter(n => validNum(n));

console.log(validNumbers);

answered Dec 10, 2019 at 22:17

Bibberty

4,7762 gold badges10 silver badges23 bronze badges

2 Comments

patstuart Over a year ago

I agree this is the best solution, but this level of Javascript is probably beyond the poster's expertise.

Bibberty Over a year ago

Yes, I should have supplied a better description of how it works.

Ivan86 · Accepted Answer · 2019-12-10 23:05:11Z

0

If I understood correctly, and assuming your other functions are correct, you can do something like below:

const findInvalidCards = (arrBatch) =>{
    let invalidCred = []
    for(let i = 0; i<arrBatch.length; i++){
        for(let j = 0; j<arrBatch[i].length; j++){
            if( !validateCred(arrBatch[i][j]) ) {  // if invalid then push to arary
                invalidCred.push(arrBatch[i][j]);
            }
        }
    }
    return invalidCred;  // return array of invalid cards
};

findInvalidCards(batch);

edited Dec 10, 2019 at 23:05

answered Dec 10, 2019 at 22:19

Ivan86

5,7182 gold badges16 silver badges30 bronze badges

Collectives™ on Stack Overflow

How to use a function on each array within an array

4 Answers 4

1 Comment

2 Comments

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

1 Comment

2 Comments

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related