Add range example

Author: aqrln

range-generator.js

@@ -0,0 +1,31 @@
+'use strict';
+
+function* range(first, second, step = 1) {
+  let current;
+  let end;
+
+  if (second === undefined) {
+    current = 0;
+    end = first;
+  } else {
+    current = first;
+    end = second;
+  }
+
+  if (step === 0) {
+    throw new Error('illegal step');
+  }
+
+  while (current < end && step > 0 ||
+         current > end && step < 0) {
+    yield current;
+    current += step;
+  }
+}
+
+console.log([
+  [...range(10)],
+  [...range(3, 18)],
+  [...range(2, 15, 2)],
+  [...range(10, 0, -1)],
+]);

range.js

@@ -0,0 +1,49 @@
+'use strict';
+
+class Range {
+  constructor(first, second, step = 1) {
+    if (second === undefined) {
+      this.start = 0;
+      this.end = first;
+    } else {
+      this.start = first;
+      this.end = second;
+    }
+
+    if (step === 0) {
+      throw new Error('illegal step');
+    }
+
+    this.step = step;
+  }
+
+  [Symbol.iterator]() {
+    const { start, end, step } = this;
+    let current = start;
+    return {
+      next() {
+        if (current === undefined) {
+          return { value: undefined, done: true };
+        }
+
+        if (current >= end && step > 0 ||
+            current <= end && step < 0) {
+          let value = current;
+          current = undefined;
+          return { value, done: true };
+        }
+
+        let value = current;
+        current += step;
+        return { value, done: false };
+      }
+    };
+  }
+}
+
+console.log([
+  [...new Range(10)],
+  [...new Range(3, 18)],
+  [...new Range(2, 15, 2)],
+  [...new Range(10, 0, -1)],
+]);