How to perform case-insensitve lookup in javascript's set?

I have a situation where I have a set of allowed strings which doesn't ensure what case they would be in. I need to validate a user input against that set. How can I achieve this?

const countries = new Set();
countries.add("USA");
countries.add("japan");

// returns false, but is there any way I could get 
//`my set to ignore case and return true?`
console.log(countries.has("usa")); 

console.log(countries.has("USA"));

How to perform case-insensitve lookup in javascript's set?

I have a situation where I have a set of allowed strings which doesn't ensure what case they would be in. I need to validate a user input against that set. How can I achieve this?

const countries = new Set();
countries.add("USA");
countries.add("japan");

// returns false, but is there any way I could get 
//`my set to ignore case and return true?`
console.log(countries.has("usa")); 

console.log(countries.has("USA"));

• javascript
• ecmascript-6
• set

• A way to achieve this is put all what you need in your set is upperCase then .has("string".toUpperCase()) – FrV Commented Apr 1, 2019 at 15:47
• 1 you can rewrite the .has method to ignore case. – arizafar Commented Apr 1, 2019 at 15:47

4 Answers 4

Just always call .toLowerCase on the string before you add it or before performing a .has check. For sure you can also abstract that into a class (if thats really necessary):

 class CaseInsensitiveSet extends Set {
   constructor(values) {
     super(Array.from(values, it => it.toLowerCase()));
   }

   add(str) {
     return super.add(str.toLowerCase());
   }

   has(str) {
     return super.has(str.toLowerCase());
   }

   delete(str) {
     return super.delete(str.toLowerCase());
   }
}

const countries = new CaseInsensitiveSet([
  "Usa",
]);

console.log(countries.has("usa")); // true

The short answer is "no". has uses SameValueZero algorithm to seek for a value's existence. See the parison table here.

If performance is not a concern, you can try two searches, one with uppercased value, and one with lowercased value, and decide whether the value actually exists.

And the better approach would be to always insert the values by converting them to uppercase/lowercase and match accordingly for existence.

Sets check the exact data you have provided. The simplest solution is to save the data in lowercase or UPPERCASE and then search over the set using the .toLoserCase() String method.

Example:

// Save data in lowecase
const set1 = new Set(['test', 'other']);

console.log(set1.has('Test'));
// expected output: false

console.log(set1.has('Other'.toLowerCase()));
// expected output: false

You can add a hasIgnoreCase() prototype on Set.

Set.prototype.hasIgnoreCase = function(str) {
  return this.has(str) || this.has(str.toUpperCase());
}

const countries = new Set();
countries.add("USA");
countries.add("japan");



// returns false, but is there any way I could get 
//`my set to ignore case and return true?`
console.log(countries.hasIgnoreCase("usa"));

console.log(countries.hasIgnoreCase("USA"));