Add .peek() method

Fixes #6

Author: sindresorhus

index.d.ts

@@ -47,6 +47,13 @@ export default class Queue<ValueType> implements Iterable<ValueType> {
 	*/
 	dequeue(): ValueType | undefined;
 
+	/**
+	Get the next value in the queue without removing it.
+
+	@returns The value or `undefined` if the queue is empty.
+	*/
+	peek(): ValueType | undefined;
+
 	/**
 	Clear the queue.
 	*/

index.js

@@ -46,6 +46,10 @@ export default class Queue {
 		return current.value;
 	}
 
+	peek() {
+		return this.#head?.value;
+	}
+
 	clear() {
 		this.#head = undefined;
 		this.#tail = undefined;

readme.md

@@ -51,6 +51,12 @@ Remove the next value in the queue.
 
 Returns the removed value or `undefined` if the queue is empty.
 
+#### `.peek()`
+
+Get the next value in the queue without removing it.
+
+Returns the value or `undefined` if the queue is empty.
+
 #### `.clear()`
 
 Clear the queue.

test.js

@@ -20,6 +20,19 @@ test('.dequeue()', t => {
 	t.is(queue.dequeue(), undefined);
 });
 
+test('.peek()', t => {
+	const queue = new Queue();
+	t.is(queue.peek(), undefined);
+	queue.enqueue('🦄');
+	t.is(queue.peek(), '🦄');
+	queue.enqueue('🌈');
+	t.is(queue.peek(), '🦄');
+	queue.dequeue();
+	t.is(queue.peek(), '🌈');
+	queue.dequeue();
+	t.is(queue.peek(), undefined);
+});
+
 test('.clear()', t => {
 	const queue = new Queue();
 	queue.clear();