How use classes in Javascript classes inside classes

Question

Code:
var base;
var preFunc = {
base = {
ConvertToAnyBase: function(number, base) {
return number.toString(base);
},
ConvertToBinary: function(number) {
return this.ConvertToAnyBase(number, 2);
},
ConvertToBase48: function(number) {
return this.ConvertToAnyBase(number, 48);
},
}
}

There would be more code but this gives error of classes inside classes how to fix it!?