var SomeObject = function(a, b){
    this.a = a;
    this.b = b
}

SomeObject.prototype.toString = function(){
    return [ this.a, this.b ].join(' ')
}

var objInstance = new SomeObject('this', 'that');

console.log(objInstance + '')                // this that
console.log(("" + objInstance).split(''))    // [ 't', 'h', 'i', 's', ' ', 't', 'h', 'a', 't' ]
console.log(objInstance.split())             // error