A method is a function attached to an object as a property.
let stringUtils = {
capitalize: function(word) {
return word.charAt(0).toUpperCase() +
word.slice(1).toLowerCase();
},
yell: function(opinion) {
return opinion.toUpperCase() + '!!!';
}
}
stringUtils.yell('i love pizza') //=> 'I LOVE PIZZA!!!'
let rectangle = {
height: 10,
width: 8,
area: function() {
return this.height * this.width;
}
}
rectangle.height //=> 10
rectangle.area() //=> 80
The keyword
this
means "this object I'm in right now"
this
Keyword is SpecialThe this
keyword is a special value that is a reference to the object that it is used within
let cardinal = {
color: 'red',
describe: function() {
return 'I am a ' + this.color + ' bird';
}
}
let blueJay = {
color: 'blue',
describe: function() {
return 'I am a ' + this.color + ' bird';
}
}
console.log(cardinal.describe());
// 'I am a red bird'
console.log(blueJay.describe());
// 'I am a blue bird'
Since JavaScript is a dynamic language, you can add methods to any object.
let rectangle = {
height: 10,
width: 8,
}
rectangle.area() //=> TypeError: rectangle.area is not a function
rectangle.area = function() {
return this.height * this.width;
}
rectangle.area() //=> 80
this
means "this object I'm in right now" which in this case is the rectanglethis.height
on the inside of the object means the same as rectangle.height
on the outside
Using the following definition:
let dog = {
name: 'Fido',
paws: 4
}
Please add a method to dog
called speak
so the following code:
console.log(dog.speak())
prints the following line:
My name is Fido and I have 4 paws!
let dog = {
name: 'Abby',
paws: 4
}
dog.speak = function() {
return "My name is " + this.name + " and I have " + this.paws + "paws"
}
You can add methods to all objects of the same type like this:
'banana'.capitalize()
//=> TypeError: 'banana'.capitalize is not a function
String.prototype.capitalize = function() {
return this.charAt(0).toUpperCase() +
this.slice(1).toLowerCase();
}
'banana'.capitalize() //=> "Banana"
String.prototype
is a special object whose properties (including methods!) are made available to all strings.
This clever trick is useful but dangerous. Don't outsmart yourself!
"Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it." - Brian Kernighan
Specifically, if you change the definition of basic types, you might introduce bugs somewhere else in your program -- possibly in code that you didn't even write yourself!
That's why extending system classes is sometimes called by the derogatory term "monkey patching".
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