Exercício andando no tabuleiro em JavaScript

AndandoNoTabuleiro.js

var Table = {
    field: [
       ['', '', ''],
       ['', '', ''],
       ['', '', '']
    ],
    position: [0,0],
    up(){
        if(this.position[0] > 0){
            this.position[0]--;
        }
        this.print();
    },
    down(){
        if(this.position[0] < this.field.length-1){
            this.position[0]++;
        }
        this.print();
    },
    left(){
        if(this.position[1] > 0){
            this.position[1]--;
        }
        this.print();        
    },
    right(){
      if(this.position[1] < this.field[this.position[0]].length-1){
            this.position[1]++;
        }
        this.print();  
    },
    print(){
        var lineStr = '';
        for(var i = 0; i < this.field.length; i++){
            var line = this.field[i];
            for(var j = 0; j < line.length; j++){
                if(this.position[0] === i && this.position[1] === j){
                    lineStr += '| X |';       
                }else{
                    lineStr += '|   |';
                }
            }
            lineStr += '\n';
        }
        console.log(lineStr);
    }
}

Table.print();