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C # tutorial
With the call() method, you can write a method that can be used on different objects
With the call()
method, you can write a method that can be used on different
objects.
In JavaScript all functions are object methods.
If a function is not a method of a JavaScript object, it is a function of the global object (see previous chapter).
The example below creates an object with 3 properties, firstName, lastName, fullName.
const person = {
firstName:"John",
lastName: "Doe",
fullName: function () {
return this.firstName + " " + this.lastName;
}
}
// This will return "John Doe":
person.fullName();
In the example above, this
refers to the person object.
Same as:
In JavaScript, the this
keyword refers to an object.
this
is being invoked (used or called).
The this
keyword refers to different objects depending on how it is used:
In an object method, this refers to the object. |
Alone, this refers to the global object. |
In a function, this refers to the global object. |
In a function, in strict mode, this is undefined . |
In an event, this refers to the element that received the event. |
Methods like call() , apply() ,
and bind() can refer this to any object. |
this
is not a variable. It is a keyword. You cannot change the value of this
.
The call()
method is a predefined
JavaScript method.
It can be used to invoke (call) a method with an owner object as an argument (parameter).
With call()
, an object can use a method belonging to another object.
This example calls the fullName method of person, using it on person1:
const person = {
fullName: function() {
return this.firstName + " " + this.lastName;
}
}
const person1 = {
firstName:"John",
lastName: "Doe"
}
const person2 = {
firstName:"Mary",
lastName: "Doe"
}
// This will return "John Doe":
person.fullName.call(person1);
This example calls the fullName method of person, using it on person2:
const person = {
fullName: function() {
return this.firstName + " " + this.lastName;
}
}
const person1 = {
firstName:"John",
lastName: "Doe"
}
const person2 = {
firstName:"Mary",
lastName: "Doe"
}
// This will return "Mary Doe"
person.fullName.call(person2);
The call()
method can accept arguments:
const person = {
fullName: function(city, country) {
return this.firstName + " " + this.lastName
+ "," + city + "," + country;
}
}
const person1 = {
firstName:"John",
lastName: "Doe"
}
person.fullName.call(person1, "Oslo", "Norway");