unshift() and shift()

mutable operation

let queue = ["person1", "person2"];

// unshift: Add to beginning
queue.unshift("person0");
console.log(queue); // ["person0", "person1", "person2"]

// shift: Remove from beginning
let firstPerson = queue.shift();
console.log(firstPerson); // "person0"
console.log(queue); // ["person1", "person2"]