function History() { this.index = 0; this.a = []; this.clear = function() { this.a = []; this.index = 0; } this.push = function(data) { if(this.index < this.a.length-1){ this.fork(); } this.index = this.a.length; this.a = this.a.slice(0,this.index); this.a.push(copy(data)); if(this.a.length > 20){ this.a.shift(); } } this.fork = function() { this.a = this.a.slice(0,this.index+1); } this.pop = function() { return this.a.pop(); } this.prev = function() { this.index = clamp(this.index-1,0,this.a.length-1); return copy(this.a[this.index]); } this.next = function() { this.index = clamp(this.index+1,0,this.a.length-1); return copy(this.a[this.index]); } function copy(data){ return data ? JSON.parse(JSON.stringify(data)) : []; } function clamp(v, min, max) { return v < min ? min : v > max ? max : v; } }