Stack

class Stack {
     constructor() {
        this.data = [];
    }
    
    peek(){
       return this.data[this.data.length - 1]; 
    }
    
    push(value) {
        this.data.push(value);
        return this;
    }
    
    pop(){
        this.data.pop();
        return this;
    }
    
    isEmpty() {
        return this.data.length === 0;
    }
}