Add exaple with sha-256 hash

tshemsedinov · tshemsedinov · commit 50448c6ae1a2 · 2017-11-14T12:56:44.000+02:00
diff --git a/JavaScript/5-sha.js b/JavaScript/5-sha.js
@@ -0,0 +1,38 @@
+'use strict';
+
+const crypto = require('crypto');
+
+const generateKey = args => {
+  const key = args.map(x => x.toString() + ':' + typeof(x)).join('|');
+  return crypto.createHash('sha256').update(key).digest('hex');
+};
+
+const memoize = fn => {
+  const cache = {};
+  return (...args) => {
+    const key = generateKey(args);
+    const val = cache[key];
+    if (val) return val;
+    const res = fn(...args);
+    cache[key] = res;
+    return res;
+  };
+};
+
+// Usage
+
+const sumSeq = (a, b) => {
+  console.log('Calculate sum');
+  let r = 0;
+  for (let i = a; i < b; i++) r += i;
+  return r;
+};
+
+const mSumSeq = memoize(sumSeq);
+
+console.log('First call mSumSeq(2, 5)');
+console.log('Value: ' + mSumSeq(2, 5));
+console.log('Second call mSumSeq(2, 5)');
+console.log('From cache: ' + mSumSeq(2, 5));
+console.log('Call mSumSeq(2, 6)');
+console.log('Calculated: ' + mSumSeq(2, 6));
