feat: add at method.

Author: ghosind

src/dynamicBuffer.ts

@@ -271,6 +271,30 @@ export class DynamicBuffer {
     return count;
   }
 
+  /**
+   * Takes an integer value and returns the item at that index, allowing for positive and negative
+   * integers. Negative integers count back from the last item in the array. Takes an integer value
+   * and returns the item at the index.
+   *
+   * ```js
+   * buf.append('Hello world');
+   * console.log(buf.at(0));
+   * // 72
+   *
+   * @param index Zero-based index of the byte in the buffer to be returned.
+   * @returns The byte at the position in the buffer.
+   */
+  at(index: number): number | undefined {
+    if (!this.buffer || index >= this.used) {
+      return undefined;
+    }
+
+    if (index >= 0) {
+      return this.buffer.at(index);
+    }
+    return this.buffer.at(index - (this.size - this.length));
+  }
+
   /**
    * Reads and returns a byte at the position `offset` in this buffer.
    *
@@ -281,7 +305,7 @@ export class DynamicBuffer {
    * ```
    *
    * @param offset Number of bytes to skip before starting to read, and the offset must satisfy
-   * between 0 and `this.length - `, default `0`.
+   * between 0 and `this.length`, default `0`.
    * @returns The byte at the position in the buffer.
    */
   read(offset: number = 0): number {

test/read.spec.ts

@@ -44,3 +44,47 @@ describe('Read tests', () => {
     });
   });
 });
+
+describe('At tests', () => {
+  it('Test at with positive index within buffer\'s length', () => {
+    const str = 'Hello world';
+    const buffer = new DynamicBuffer(str);
+
+    for (let i = 0; i < str.length; i += 1) {
+      assert.equal(buffer.at(i), str.charCodeAt(i));
+    }
+  });
+
+  it('Test at with positive index greater than buffer\'s length', () => {
+    const str = 'Hello world';
+    const buffer = new DynamicBuffer(str);
+
+    assert.equal(buffer.at(str.length), undefined);
+  });
+
+  it('Test at with a negative index', () => {
+    const str = 'Hello world';
+    const buffer = new DynamicBuffer(str);
+
+    for (let i = 0; i < str.length; i += 1) {
+      assert.equal(buffer.at(0 - str.length + i), str.charCodeAt(i));
+    }
+  });
+
+  it('Test at with negative index more than buffer\'s length', () => {
+    const str = 'Hello world';
+    const buffer = new DynamicBuffer(str);
+
+    assert.equal(buffer.at(-str.length - 1), undefined);
+  });
+
+  it('Test at with specified buffer size and negative index', () => {
+    const str = 'Hello world';
+    const buffer = new DynamicBuffer(str, { size: str.length });
+
+    for (let i = 0; i < str.length; i += 1) {
+      assert.equal(buffer.at(0 - str.length + i), str.charCodeAt(i));
+    }
+    assert.equal(buffer.at(-str.length - 1), undefined);
+  });
+});