Why does this code return bar twice, not foo then bar?
function Person(name) {
if (name) this.options.name = name;
}
Person.prototype.options = {
name: "Default name"
};
var foo = new Person("foo");
var bar = new Person("bar");
console.log(foo.options.name);
console.log(bar.options.name);does it because of the reference and can you guys explain
thanks to all people who answered this question.
1- both foo and bar are pointing to the same object, that called options.
2- they are pointing to the same passed value called name.
3- both foo and bar are objects, so they are references.
4- and they are containing object called options and which also reference.
5- so when we change name value in options object in any one of foo it will be changed to options object name value in all created objects funding Person function.
I think this is the answere
Because when you've instantiated foo and bar they made a shallow copy of Person.prototype.options object.
function Person(name) {
if (name) this.options.name = name;
}
Person.prototype.options = {
name: "Default name"
};
var foo = new Person("foo");
var bar = new Person("bar");
// are foo.options and bar.options pointing to the same options object?
console.log(foo.options===bar.options)As you can see foo.options===bar.options returns true.
this.optionsrefersoptionsobject in the prototype, that's a common object for all the instances ofPerson. Make it like this:this.name = name || this.options.name;, that way you can read a default name from options, and give an individual name for every instance if it is passed.console.log( "Object.is: %o", Object.is( foo.options, bar.options ) );- it will print"Object.is: true.options = { name: "Default name" }; foo = options; bar = options; foo.name = "foo"; bar.name = "bar";basically the same as what your code does. Modifying the same object leads to...modifying the same object.Object.assign) when thePersonconstructor runs. I'll admit that I've forgotten how to useprototypesuch that instances don't share state...this.options = Object.create(this.options)in the constructor, to have nested inheriting objects, but I wouldn't recommend it)