Edit in JSFiddle

var a = new Array(3);
        
for (var i = 0, length = a.length; i < length; i++) {

    a[i] = []
    a[i][0] = 'a';
    a[i][1] = 'b';
    a[i][2] = 'c';
}

console.log(a[0][0]);
console.log(a[0][1]);
console.log(a[0][2]);