Feat: Add LRANGE support (#335)

* Create lrange.js

* Create test file for LRANGE

* Lining issue fix: no-param-reassign

* Add lrange to export list

* Update lrange.js

src/commands/index.js

@@ -44,6 +44,7 @@ export * from './lpop';
 export * from './lpopBuffer';
 export * from './lpush';
 export * from './lpushx';
+export * from './lrange';
 export * from './lrem';
 export * from './lset';
 export * from './mget';

src/commands/lrange.js

@@ -0,0 +1,27 @@
+/**
+ * Returns the specified elements of the list stored at key. The offsets start and stop are zero-based indexes, with 0 being the first element of the list (the head of the list), 1 being the next element and so on.
+ * These offsets can also be negative numbers indicating offsets starting at the end of the list. For example, -1 is the last element of the list, -2 the penultimate, and so on.
+ * 
+ * @param {string} key
+ * @param {string} start Start index
+ * @param {string} end End index (included in returned range)
+ * @return {Array} An array in the defined range
+ */
+export function lrange(key, s, e) {
+  if (this.data.has(key) && !(this.data.get(key) instanceof Array)) {
+    throw new Error(`Key ${key} does not contain a list`);
+  }
+  let start = parseInt(s, 10);
+  let end = parseInt(e, 10);
+
+  const list = this.data.get(key) || [];
+
+  if (start < 0) {
+    start = list.length + start;
+  }
+  if (end < 0) {
+    end = list.length + end;
+  }
+
+  return list.slice(start, end + 1);
+}

test/commands/lrange.js

@@ -0,0 +1,67 @@
+import expect from 'expect';
+
+import MockRedis from '../../src';
+
+describe('lrange', () => {
+  it('should return first 3 items', () => {
+    const redis = new MockRedis({
+      data: {
+        foo: ['1', '2', '3', '4', '5'],
+      },
+    });
+
+    return redis
+      .lrange('foo', 0, 2)
+      .then(res => expect(res).toEqual(['1', '2', '3']));
+  });
+
+  it('should return last 3 items', () => {
+    const redis = new MockRedis({
+      data: {
+        foo: ['1', '2', '3', '4', '5'],
+      },
+    });
+
+    return redis
+      .lrange('foo', -3, -1)
+      .then(res => expect(res).toEqual(['3', '4', '5']));
+  });
+
+  it('should return last all items on larger numbers', () => {
+    const redis = new MockRedis({
+      data: {
+        foo: ['1', '2', '3', '4', '5'],
+      },
+    });
+
+    return redis
+      .lrange('foo', 0, 100)
+      .then(res => expect(res).toEqual(['1', '2', '3', '4', '5']));
+  });
+
+  it('should return empty array if out-of-range', () => {
+    const redis = new MockRedis({
+      data: {
+        foo: ['1', '2', '3', '4', '5'],
+      },
+    });
+
+    return redis
+      .lrange('foo', 10, 100)
+      .then(res => expect(res).toEqual([]));
+  });
+
+  it('should throw an exception if the key contains something other than a list', () => {
+    const redis = new MockRedis({
+      data: {
+        foo: 'not a list',
+      },
+    });
+
+    return redis
+      .lrange('foo', 0, 2)
+      .catch(err =>
+        expect(err.message).toBe('Key foo does not contain a list')
+      );
+  });
+});