feat: add length getter.

- Add length getter to getting the number of in-use bytes.
- Update test cases to testing length getter.
- Update readme.

Author: ghosind

README.md

@@ -32,7 +32,7 @@ yarn add dynamic-buffer
 2. Creates `DynamicBuffer` instance with default initial size or the specific size:
 
   ```ts
-  const buffer = new DynamicBuffer({ size: 12 });
+  const buffer = new DynamicBuffer();
   ```
 
 3. Appends data into buffer:
@@ -42,9 +42,11 @@ yarn add dynamic-buffer
   buffer.append('world!');
   ```
 
-4. Exports data to string or builtin buffer object:
+4. Exports data to string or builtin buffer object without unused bytes:
 
   ```ts
+  console.log(buffer.length);
+  // 12
   const buf = buffer.toBuffer();
   console.log(buf.toString());
   // Hello world!

src/dynamicBuffer.ts

@@ -85,6 +85,13 @@ export class DynamicBuffer {
     }
   }
 
+  /**
+   * Returns the number of the used bytes in this buffer.
+   */
+  get length() {
+    return this.used;
+  }
+
   /**
    * Appends string to this buffer according to the character encoding.
    *

test/dynamicBuffer.spec.ts

@@ -10,6 +10,7 @@ describe('Initialization tests', () => {
 
     assert.equal(Reflect.get(buffer, 'size'), Reflect.get(buffer, 'DefaultInitialSize'));
     assert.notEqual(Reflect.get(buffer, 'buffer'), undefined);
+    assert.equal(buffer.length, 0);
   });
 
   it('Test initializing with zero size', () => {
@@ -53,6 +54,7 @@ describe('Append tests', () => {
     count = buffer.append(str);
     assert.equal(count, str.length);
     assert.equal(buffer.toString(), 'Hello world');
+    assert.equal(buffer.length, 'Hello world'.length);
   });
 
   it('Test appending empty string', () => {