A JavaScript string stores a series of characters like “John Doe”.
A string can be any text inside double or single quotes:
let carName1 = "Volvo XC60";
let carName2 = 'Volvo XC60';
String indexes are zero-based:
The first character is in position 0, the second in 1, and so on. Continue reading JavaScript String Reference
The length property returns the length of a string:
let text = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; let length = text.length;
Strings are for storing text
Strings are written with quotes
A JavaScript string is zero or more characters written inside quotes.
let text = "John Doe";
HTML events are “things” that happen to HTML elements.
When JavaScript is used in HTML pages, JavaScript can “react” on these events.
An HTML event can be something the browser does, or something a user does.
Here are some examples of HTML events:
Often, when events happen, you may want to do something. Continue reading JavaScript Events
Sometimes we need to create many objects of the same type.
To create an object type we use an object constructor function.
It is considered good practice to name constructor functions with an upper-case first letter.
function Person(first, last, age, eye) {
this.firstName = first;
this.lastName = last;
this.age = age;
this.eyeColor = eye;
}
Displaying a JavaScript object will output [object Object].
// Create an Object
const person = {
name: "John",
age: 30,
city: "New York"
};
document.getElementById("demo").innerHTML = person;
Object methods are actions that can be performed on objects.
A method is a function definition stored as a property value.
| Property | Value |
|---|---|
| firstName | John |
| lastName | Doe |
| age | 50 |
| eyeColor | blue |
| fullName | function() {return this.firstName + ” ” + this.lastName;} |
const person = {
firstName: "John",
lastName: "Doe",
id: 5566,
fullName: function() {
return this.firstName + " " + this.lastName;
}
};
In the example above, this refers to the person object :
this.firstName means the firstName property of person. Continue reading JavaScript Object Methods
Properties are the most important part of JavaScript objects.
Properties can be changed, added, deleted, and some are read only.
The syntax for accessing the property of an object is:
// objectName.property let age = person.age; or //objectName["property"] let age = person["age"]; or //objectName[expression] let age = person[x];
person.firstname + " is " + person.age + " years old."; person["firstname"] + " is " + person["age"] + " years old."; let x = "firstname"; let y = "age"; person[x] + " is " + person[y] + " years old.";
A real life car has properties like weight and color:
car.name = Fiat, car.model = 500, car.weight = 850kg, car.color = white.
Car objects have the same properties, but the values differ from car to car.
A real life car has methods like start and stop:
car.start(), car.drive(), car.brake(), car.stop().
Car objects have the same methods, but the methods are performed at different times. Continue reading JavaScript Objects
A JavaScript function is a block of code designed to perform a particular task.
A JavaScript function is executed when “something” invokes it (calls it).
// Function to compute the product of p1 and p2
function myFunction(p1, p2) {
return p1 * p2;
}
A JavaScript function is defined with the function keyword, followed by a name, followed by parentheses ().
Function names can contain letters, digits, underscores, and dollar signs (same rules as variables). Continue reading JavaScript Functions