1class BrowserHistory {
2    constructor(url) {
3        this.history = [];
4        this.pointer = 0;
5        if (url !== undefined) {
6            this.history.push(url);
7        }
8    }
9
10    visit(url) {
11        this.history.length = this.pointer + 1;
12        this.history.push(url);
13        this.pointer++;
14    }
15    
16    back() {
17        this.pointer = Math.max(0, --this.pointer);
18    }
19
20    forward() {
21        this.pointer = Math.min(this.history.length - 1, ++this.pointer);
22    }
23}