feat(solution): javascript-non-repeating

challenges/first-non-repeating-character/solutions/javascript-non-repeating/README.md

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+# javascript-non-repeating - first-non-repeating-character
+
+Programming language : JavaScript
+
+Created by [@Divlo](https://github.com/Divlo) on 15 November 2020.

challenges/first-non-repeating-character/solutions/javascript-non-repeating/solution.js

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+/**
+ * @param {string} string
+ */
+function solution (string) {
+  const lettersCount = {}
+  for (let index = 0; index < string.length; index++) {
+    const character = string[index]
+    if (lettersCount[character] == null) {
+      lettersCount[character] = {
+        total: 1,
+        firstIndex: index,
+        value: character
+      }
+    } else {
+      lettersCount[character].total += 1
+    }
+  }
+
+  let result = null
+  for (const character in lettersCount) {
+    const characterObject = lettersCount[character]
+    if (characterObject.total === 1) {
+      if (result == null) {
+        result = characterObject
+      } else if (characterObject.firstIndex < result.firstIndex) {
+        result = characterObject
+      }
+    }
+  }
+
+  if (result == null) {
+    return ''
+  }
+  return result.value
+}
+
+module.exports = solution