let and const examples

chapter02/src/let_const.js

@@ -0,0 +1,40 @@
+/* @flow */
+/* eslint-disable no-unused-vars, no-constant-condition, no-var, prefer-const */
+
+{
+    let w = 0;
+}
+console.log(w); // error: w is not defined!
+
+let x = 1;
+{
+    let x = 99;
+}
+console.log(x); // still 1;
+
+let y = 2;
+for (let y = 999; false; ) {
+    /* nothing! */
+}
+console.log(y); // still 2;
+
+const z = 3;
+z = 999; // error!
+
+// Countdown to zero?
+var delay = 0;
+for (var i = 10; i >= 0; i--) {
+    delay += 1000;
+    setTimeout(() => {
+        console.log(i + (i > 0 ? "..." : "!"));
+    }, delay);
+}
+
+delay = 0;
+for (let i = 10; i >= 0; i--) {
+    // minimal fix!
+    delay += 1000;
+    setTimeout(() => {
+        console.log(i + (i > 0 ? "..." : "!"));
+    }, delay);
+}