Added string subsequence in JS (#196)

* Added string subsequence in js

* remove extra line

strings/README.md

@@ -18,6 +18,7 @@
 ### JavaScript
 
 1. [Palindrome Check](js/palindrome.js)
+2. [All subsequences](js/sequence.js)
 
 ### Java
 

strings/js/sequence.js

@@ -0,0 +1,44 @@
+var list = [];
+
+const subsequence = (input, output = '') => {
+    if (input === "") {
+        if (output !== '' && !list.includes(output)) list.push(output);
+        return;
+    }
+
+    subsequence(input.substr(1), output + input.charAt(0));
+    subsequence(input.substr(1), output);
+}
+
+subsequence('abc');
+console.log('abc', list);
+list = [];
+
+subsequence('aaa');
+console.log('aaa', list);
+list = [];
+
+subsequence('hello');
+console.log('hello', list);
+
+/*
+    to run the file:
+        Node sequence.js
+
+    result
+        abc [
+            'abc', 'ab',
+            'ac',  'a',
+            'bc',  'b',
+            'c'
+            ]
+        aaa [ 'aaa', 'aa', 'a' ]
+        hello [
+            'hello', 'hell', 'helo', 'hel',
+            'heo',   'he',   'hllo', 'hll',
+            'hlo',   'hl',   'ho',   'h',
+            'ello',  'ell',  'elo',  'el',
+            'eo',    'e',    'llo',  'll',
+            'lo',    'l',    'o'
+        ]
+*/