feat: add copyWithin method.

Author: ghosind

src/dynamicBuffer.ts

@@ -376,6 +376,26 @@ export class DynamicBuffer {
     return this.buffer.copy(target, targetStart, sourceStart, sourceEnd);
   }
 
+  /**
+   * Returns the this buffer after copying a section of the buffer identified by start and end
+   * to the same buffer starting at position target.
+   *
+   * @param target If target is negative, it is treated as length+target where length is the
+   * length of the array.
+   * @param start If start is negative, it is treated as length+start. If end is negative, it
+   * is treated as length+end.
+   * @param end If not specified, length of the this object is used as its default value.
+   */
+  copyWithin(target: number, start: number, end: number = this.length): DynamicBuffer {
+    if (!this.buffer || this.length === 0) {
+      return this;
+    }
+
+    this.buffer.subarray(0, this.length).copyWithin(target, start, end);
+
+    return this;
+  }
+
   /**
    * Creates and returns an iterator of key(index) and value(byte) pairs from this buffer.
    *

test/array.spec.ts

@@ -3,6 +3,21 @@ import { describe, it } from 'mocha';
 
 import { DynamicBuffer } from '../src';
 
+describe('CopyWithin tests', () => {
+  it('Test copyWithin', () => {
+    const buf = new DynamicBuffer('abcde');
+
+    assert.equal(buf.copyWithin(0, 3, 4).toString(), 'dbcde');
+    assert.equal(buf.copyWithin(1, 3).toString(), 'ddede');
+  });
+
+  it('Test copyWithin of empty buffer', () => {
+    const buf = new DynamicBuffer();
+
+    assert.equal(buf.copyWithin(0, 3, 4).toString(), '');
+  });
+});
+
 describe('Every tests', () => {
   it('Test every', () => {
     const buf1 = new DynamicBuffer('hello');