check whether string is an isogram or not

snippets/isIsogram.md

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+---
+title: isIsogram
+tags: string, intermediate
+---
+
+Creates a function that accepts a string parameter and output whether its an isogram or not.
+
+- Use `String.toLowerCase()` to convert the string to lowercase letters.
+- Use `String.prototype.split()`, `String.prototype.indexOf()` and `Array.prototype.every()` to split the string into substrings, run a test for all the elements in that array and finally return the index of first occurence of a specified value in a string.
+- Function returns true if the string is an isogram (that is no letter is repeated) else returns false.
+- Returns false is called with no parameter.
+
+```js
+const isIsogram = (str = null) => {
+  if(str == null) return false;
+  str = str.toLowerCase();
+  return str.split("").every((c, i) => str.indexOf(c) === i);
+}		
+```
+
+```js
+isIsogram("Dermatoglyphics"); // true
+isIsogram("aba"); // false
+isIsogram("moOse"); // false
+isIsogram(); // false
+```