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Tommy

ONLY_DIGITS = "^[0-9]*$";

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Tommy

Here is a better and simpler way. formatCreditCardNumber(unformattedNumber) { let pureNumber = unformattedNumber.split(" ").join(""); let pureNumberArray = pureNumber.split(""); let formattedNumberArray = []; for(let i = 0; i < pureNumberArray.length; i++){ if(!pureNumberArray[i].match(ONLY_DIGITS)){ return; } if (i != 0 && i % 4 === 0){ formattedNumberArray.push(" "); } formattedNumberArray.push(pureNumberArray[i]); } return: formattedNumberArray.join(""); }