JavaScript Array.every() does not work the way I expected

I have been tasked with writing a basic check for GUID validity without using regex. So all I'm doing is checking if the non-dash characters in the guid string are hexa digits.

const isValidGUIDChar = (char) =>  !isNaN(+char) || "abcdef".includes(char.toLowerCase());

// let guid = "123";
// let guid = "abc"
let guid = "abc123";

let isGuidValid = guid.replaceAll('-', '').length === 32 && guid.split().every(isValidGUIDChar);

console.log(isGuidValid);  // returns true for either 'abc' or '123' but false for 'abc123'

The results, mention in ment above are counter-intuitive. The every() method seems to evaluate to:

"(every character must either be numeric), or (every character must be from among 'abcdef')",

whereas what I need, and what seems intuitive, would be for it to evaluate to:

"(every character) must (either be numeric from among 'abcdef')"

How can I acplish the latter?

JavaScript Array.every() does not work the way I expected

I have been tasked with writing a basic check for GUID validity without using regex. So all I'm doing is checking if the non-dash characters in the guid string are hexa digits.

const isValidGUIDChar = (char) =>  !isNaN(+char) || "abcdef".includes(char.toLowerCase());

// let guid = "123";
// let guid = "abc"
let guid = "abc123";

let isGuidValid = guid.replaceAll('-', '').length === 32 && guid.split().every(isValidGUIDChar);

console.log(isGuidValid);  // returns true for either 'abc' or '123' but false for 'abc123'

The results, mention in ment above are counter-intuitive. The every() method seems to evaluate to:

"(every character must either be numeric), or (every character must be from among 'abcdef')",

whereas what I need, and what seems intuitive, would be for it to evaluate to:

"(every character) must (either be numeric from among 'abcdef')"

How can I acplish the latter?

• javascript
• ecmascript-6

Share Follow edited Aug 18, 2021 at 19:23 Roko C. Buljan 207k4141 gold badges328328 silver badges340340 bronze badges asked Aug 18, 2021 at 17:50 PakiPatPakiPat 1,08511 gold badge1616 silver badges2828 bronze badges 11

• Humm ... isn't "0123456789abcdef" shorter than !isNaN(+char) || "abcdef" ? Also see this: length === 32 – Roko C. Buljan Commented Aug 18, 2021 at 17:54
• 1 You've just forgotten to give split a separator, so you get a one-element array with the entire string in it, so char is the entire string. More: developer.mozilla/en-US/docs/Web/JavaScript/Reference/… If you pass it "" (or, in modern code, use [...thestring]), the check works. – T.J. Crowder Commented Aug 18, 2021 at 17:55
• 2 Also, instead of guid.split("") (which BTW is missing a "") you could do just [...guid] – Roko C. Buljan Commented Aug 18, 2021 at 17:58
• 2 @T.J.Crowder yes, but that is not a problem with isValidGUIDChar or even the .every. Also, they should not be showing code that is an obvious problem that they've "skipped over" themselves. – crashmstr Commented Aug 18, 2021 at 18:00
• 1 @crashmstr - Yeah, bad phrasing on my part in my reply to you. I should have said "To see the problem the OP thinks they have..." :-) – T.J. Crowder Commented Aug 18, 2021 at 18:01

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2 Answers 2

Sorted by: Reset to default 5

• Your .split() is missing "" (BTW, use [...guid] with Spread instead)
• Make sure you actually test with 32 char after! you replace all dashes
• Use it as a function isGuidValid(guid) - reusability, remember?

const isHEX = (ch) => "0123456789abcdef".includes(ch.toLowerCase());

const isGuidValid = (guid) => {
  guid = guid.replaceAll("-", ""); // Format it first!
  return guid.length === 32 && [...guid].every(isHEX);
};

console.log(isGuidValid("adec3dc3-7025-4905-b584-d9e64117f2fd"));  // true
console.log(isGuidValid("adec3dc3-7025-4905-b584-d9e64117f2fz"));  // false
console.log(isGuidValid("adec3dc3-7025-4905-b584-d9e64117f2f"));   // false

A more robust approach, taking in consideration the RFC4122 treating a GIUD/UUID as groups of 8-4-4-4-12 codepoint chars each would be:

const isHEX = h => !isNaN(parseInt(h, 16));
const RFC4122Len = [8, 4, 4, 4, 12];

const isGuidValid = (guid) => {

  // Must have 36 Chars per codepoint (32 + 4 dashes)
  const codePointLenght = [...guid].length;
  if (codePointLenght !== 36) return false;

  // Must have 5 groups
  const groups = guid.split("-");
  if (groups.length !== 5) return false;

  // RFC defines 5 groups of 8-4-4-4-12 codepoints chars each
  const lenMatch = groups.map(gr => [...gr].length).every((len, i) => len === RFC4122Len[i]);
  if (!lenMatch) return false;

  // Finally join groups (without the "-" separators and check for each char is HEX)
  return [...(groups.join(""))].every(isHEX);
};

console.log(isGuidValid("adec3dc3-7025-4905-b584-d9e64117f2fd")); // true
console.log(isGuidValid("adec3dc3-7025-4905-b584-d9e64117f2fz")); // false
console.log(isGuidValid("adec3dc3-7025-4905-b584-d9e64117f2f"));  // false

There's more to make it fully RFC4122 pliant but you got the general idea.

To check if the characters are hex digits just use this 3 lines :

 function isHex(h)
 {
    let a = parseInt(h, 16);

    return a.toString(16) === h;
 }