I was reading an article. It is related to javascript. Here, is a code sample from the article. Please look at below.
function customobject(){
this.value = 2;
}
customobject.prototype.inc = function(){
this.value++;
}
function changer(func){
func();
}
var o = new customobject();
alert(o.value);
o.inc();
alert(o.value);
changer(o.inc);
alert(o.value); My question is Why is the value for "o.value" unchanged when changer(o.inc) is called ?
o.inc is just a reference to the anonymous function:
function() {
this.value++;
}
Whereas this is the scope in which the function is executed. So when you run changer(o.inc), this is actually pointing to the global, in browsers it's window. It doesn't necessarily have anything to do with o.
You could bind the scope like this:
function changer(func, scope){
func.call(scope); // or apply
}
changer(o.inc, o);
Or simply:
function changer(func){
func();
}
changer(o.inc.bind(o));
The problem is because Function does not save instance for objects. You have to pass the object as argument so call your function, like this.
function customobject(){
this.value = 2;
}
customobject.prototype.inc = function(){
this.value++;
}
function changer(o){
o.inc();
}
var o = new customobject();
console.log(o.value); //It has to print 2
o.inc(); //Increment to 3
console.log(o.value); //It has to print 3
changer(o); //Increment to 4
console.log(o.value); //It has to print 4
thisand you will see what happens. the problem is that you callincwithout the this context. If you want to make it work you have to dochanger(o.inc.bind(o)). bind doc