task firstNonRepeatingLetter (from codewars)

katas/first-non-repeating-letter/first-non-repeating-letter.js

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+function firstNonRepeatingLetter(string) {
+  // Add your code here
+}

katas/first-non-repeating-letter/first-non-repeating-letter_test.js

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+describe('FirstNonRepeatingLetter function', function() {
+  it('should return result correctly', function() {
+    expect(firstNonRepeatingLetter('a')).toEqual('a');
+    expect(firstNonRepeatingLetter('stress')).toEqual('t');
+    expect(firstNonRepeatingLetter('moonmen')).toEqual('e');
+  });
+
+  it('should return empty string if string contains all repeating characters', function() {
+    expect(firstNonRepeatingLetter('aaaaaaa')).toEqual('');
+  });
+});

katas/first-non-repeating-letter/readme.md

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+####Description:
+
+Write a function named firstNonRepeatingCharacter that takes a string input, and returns the first character that is not repeated anywhere in the string.
+
+For example, if given the input 'stress', the function should return 't', since the letter t only occurs once in the string, and occurs first in the string.
+
+As an added challenge, upper- and lowercase letters are considered the same character, but the function should return the correct case for the initial letter.
+
+If a string contains all repeating characters, it should return the empty string ("").
+
+####Example:
+
+```js
+
+firstNonRepeatingCharacter('sTreSS') // 'T'
+
+```
+
+See [tests in first-non-repeating-letter_test.js](https://github.com/AlexVvx/code-wars/tree/master/katas/first-non-repeating-letter/first-non-repeating-letter_test.js)
+
+Good luck
+
+#####[Original Kata](https://www.codewars.com/kata/first-non-repeating-letter)