Check if string contains only digits

Breaking down the regex

The regular expression ^\d+$ is made up of:

• ^ signifies start of the string, like a race flag.
• \d+ matches one or more digits (0-9), the racetrack.
• $ represents the end of the string, our finish line.

In combination, these elements ensure that every character within the string bounds is a digit.

Adapting the regex

While ^\d+$ is a one-size-fits-all solution, sometimes we need a custom fit:

• Decimal numbers: ^\d+(\.\d+)?$ permits decimal points. Don't float away!
• Numbers with commas : ^\d{1,3}(,\d{3})*$ accepts formats like "1,000" and "100". Cashier-approved!
• Spaces: To handle leading or trailing spaces, use \s* as in ^\s*\d+\s*$.

Be sure to adjust your regex for specific use cases—think of it as your personal Swiss Army knife.

A reusable function

Increase your code reuse by extending String.prototype:

String.prototype.isDigitsOnly = function() {
  return /^\d+$/.test(this);  // Like James Bond, it likes its digits shaken, not stirred!
};
  
'12345'.isDigitsOnly(); // more truth than a lie detector!  It's true.
'12e45'.isDigitsOnly(); // false - it's sneaky, but we're sneakier!
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Ensure to dodge naming conflicts when extending native prototypes. You don't want to step on any toes!

Beware of the disguised

Being ready for surprises is key. Here's a few places where patchy skies might lurk:

• isNaN(): Unreliable as it stumbles upon strings like " " or "123e-1", returning false.
• parseInt() or parseFloat(): These guys will convert as much of the string to a number as they can, perfect for a heist but not for validation.
• + operator: Changing the type of a variable like a master of disguise can lead to false negatives.

Trust regex to stand guard, as it provides accurate matching and predictable results.

Regex – The knight in shining armor

Expand your use of regex to cover:

• Credit card formats: ^(?:\d{4}-){3}\d{4}$ screens card numbers like "1234-5678-9012-3456".
• ZIP code formats: ^\d{5}(-\d{4})?$ accepts 5-digit ZIP codes with 4-digit extension.

Regex, like a faithful knight, will always come to your rescue!

The no-regex path

If regex isn't your thing, get the job done using an array method:

const isDigitsOnly = (str) => str.split('').every(char => char >= '0' && char <= '9');


It’s a turtle race compared to regex, but for readability, some might say it's the hare's pal!

Testing your patterns

To vet your regex, utilize tools like regex101.com. Test against a variety of inputs to ensure precise results:

12345        ✔️ All-clear! Pure digits.
123.45       ❌ Fooled ya! Contains a hidden dot.
12e45        ❌ Almost had us! Notation isn't all digits.