Complete RegExp Object Reference

For a complete reference of all the properties and methods that can be used with the RegExp object, go to our complete RegExp object reference.

The reference contains a brief description and examples of use for each property and method!

What is RegExp?

A regular expression is an object that describes a pattern of characters.

When you search in a text, you can use a pattern to describe what you are searching for.

A simple pattern can be one single character.

A more complicated pattern can consist of more characters, and can be used for parsing, format checking, substitution and more.

Regular expressions are used to perform powerful pattern-matching and “search-and-replace” functions on text.

Syntax

• pattern specifies the pattern of an expression
• modifiers specify if a search should be global, case-sensitive, etc.

RegExp Modifiers

Modifiers are used to perform case-insensitive and global searches.

The i modifier is used to perform case-insensitive matching.

The g modifier is used to perform a global match (find all matches rather than stopping after the first match).

test()

The test() method searches a string for a specified value, and returns true or false, depending on the result.

The following example searches a string for the character “e”:

exec()

The exec() method searches a string for a specified value, and returns the text of the found value. If no match is found, it returns null.

The following example searches a string for the character “e”:

source form: w3schools

For a complete reference of all the properties and methods that can be used with the Math object, go to our complete Math object reference.

The reference contains a brief description and examples of use for each property and method!

Math Object

The Math object allows you to perform mathematical tasks.

The Math object includes several mathematical constants and methods.

Syntax for using properties/methods of Math:

Note: Math is not a constructor. All properties and methods of Math can be called by using Math as an object without creating it.

Mathematical Constants

JavaScript provides eight mathematical constants that can be accessed from the Math object. These are: E, PI, square root of 2, square root of 1/2, natural log of 2, natural log of 10, base-2 log of E, and base-10 log of E.

You may reference these constants from your JavaScript like this:

Mathematical Methods

In addition to the mathematical constants that can be accessed from the Math object there are also several methods available.

The following example uses the round() method of the Math object to round a number to the nearest integer:

The code above will result in the following output:

The following example uses the random() method of the Math object to return a random number between 0 and 1:

The code above can result in the following output:

The following example uses the floor() and random() methods of the Math object to return a random number between 0 and 10:

The code above can result in the following output:

source form: w3schools

For a complete reference of all the properties and methods that can be used with the Boolean object, go to our complete Boolean object reference.

The reference contains a brief description and examples of use for each property and method!

Create a Boolean Object

The Boolean object represents two values: “true” or “false”.

The following code creates a Boolean object called myBoolean:

If the Boolean object has no initial value, or if the passed value is one of the following:

• 0
• -0
• null
• “”
• false
• undefined
• NaN

the object is set to false. For any other value it is set to true (even with the string “false”)!

source form: w3schools

For a complete reference of all the properties and methods that can be used with the Array object, go to our complete Array object reference.

The reference contains a brief description and examples of use for each property and method!

What is an Array?

An array is a special variable, which can hold more than one value, at a time.

If you have a list of items (a list of car names, for example), storing the cars in single variables could look like this:

However, what if you want to loop through the cars and find a specific one? And what if you had not 3 cars, but 300?

The best solution here is to use an array!

An array can hold all your variable values under a single name. And you can access the values by referring to the array name.

Each element in the array has its own ID so that it can be easily accessed.

Create an Array

An array can be defined in three ways.

The following code creates an Array object called myCars:

1:

2:

3:

Note: If you specify numbers or true/false values inside the array then the variable type will be Number or Boolean, instead of String.

Access an Array

You can refer to a particular element in an array by referring to the name of the array and the index number. The index number starts at 0.

The following code line:

will result in the following output:

Modify Values in an Array

To modify a value in an existing array, just add a new value to the array with a specified index number:

Now, the following code line:

will result in the following output:

source form: w3schools

For a complete reference of all the properties and methods that can be used with the Date object, go to our complete Date object reference.

The reference contains a brief description and examples of use for each property and method!

Create a Date Object

The Date object is used to work with dates and times.

Date objects are created with the Date() constructor.

There are four ways of instantiating a date:

Most parameters above are optional. Not specifying, causes 0 to be passed in.

Once a Date object is created, a number of methods allow you to operate on it. Most methods allow you to get and set the year, month, day, hour, minute, second, and milliseconds of the object, using either local time or UTC (universal, or GMT) time.

All dates are calculated in milliseconds from 01 January, 1970 00:00:00 Universal Time (UTC) with a day containing 86,400,000 milliseconds.

Some examples of instantiating a date:

Set Dates

We can easily manipulate the date by using the methods available for the Date object.

In the example below we set a Date object to a specific date (14th January 2010):

And in the following example we set a Date object to be 5 days into the future:

Note: If adding five days to a date shifts the month or year, the changes are handled automatically by the Date object itself!

Compare Two Dates

The Date object is also used to compare two dates.

The following example compares today’s date with the 14th January 2100:

source form: w3schools

For a complete reference of all the properties and methods that can be used with the String object, go to our complete String object reference.

The reference contains a brief description and examples of use for each property and method!

String object

The String object is used to manipulate a stored piece of text.

Examples of use:

The following example uses the length property of the String object to find the length of a string:

The code above will result in the following output:

The following example uses the toUpperCase() method of the String object to convert a string to uppercase letters:

The code above will result in the following output:

source form: w3schools

An Object Based Programming language allows you to define your own objects and make your own variable types.

Object Based Programming

JavaScript is an Object Based Programming language, and allows you to define your own objects and make your own variable types.

However, creating your own objects will be explained later, in the Advanced JavaScript section. We will start by looking at the built-in JavaScript objects, and how they are used. The next pages will explain each built-in JavaScript object in detail.

Note that an object is just a special kind of data. An object has properties and methods.

Properties

Properties are the values associated with an object.

In the following example we are using the length property of the String object to return the number of characters in a string:

The output of the code above will be:

Methods

Methods are the actions that can be performed on objects.

In the following example we are using the toUpperCase() method of the String object to display a text in uppercase letters:

The output of the code above will be:

source form: w3schools

Earlier in this tutorial we have seen that JavaScript has several built-in objects, like String, Date, Array, and more. In addition to these built-in objects, you can also create your own.

An object is just a special kind of data, with a collection of properties and methods.

Let’s illustrate with an example: A person is an object. Properties are the values associated with the object. The persons’ properties include name, height, weight, age, skin tone, eye color, etc. All persons have these properties, but the values of those properties will differ from person to person. Objects also have methods. Methods are the actions that can be performed on objects. The persons’ methods could be eat(), sleep(), work(), play(), etc.

Properties

The syntax for accessing a property of an object is:

You can add properties to an object by simply giving it a value. Assume that the personObj already exists – you can give it properties named firstname, lastname, age, and eyecolor as follows:

The code above will generate the following output:

Methods

An object can also contain methods.

You can call a method with the following syntax:

Note: Parameters required for the method can be passed between the parentheses.

To call a method called sleep() for the personObj:

Creating Your Own Objects

There are different ways to create a new object:

1. Create a direct instance of an object

The following code creates a new instance of an object, and adds four properties to it:

alternative syntax (using object literals):

Adding a method to the personObj is also simple. The following code adds a method called eat() to the personObj:

2. Create an object constructor

Create a function that construct objects:

Inside the function you need to assign things to this.propertyName. The reason for all the “this” stuff is that you’re going to have more than one person at a time (which person you’re dealing with must be clear). That’s what “this” is: the instance of the object at hand.

Once you have the object constructor, you can create new instances of the object, like this:

You can also add some methods to the person object. This is also done inside the function:

Note that methods are just functions attached to objects. Then we will have to write the newlastname() function:

The newlastname() function defines the person’s new last name and assigns that to the person. JavaScript knows which person you’re talking about by using “this.”. So, now you can write: myMother.newlastname(“Doe”).

source form: w3schools

JavaScript can be used to validate data in HTML forms before sending off the content to a server.

Form data that typically are checked by a JavaScript could be:

• has the user left required fields empty?
• has the user entered a valid e-mail address?
• has the user entered a valid date?
• has the user entered text in a numeric field?

Required Fields

The function below checks if a field has been left empty. If the field is blank, an alert box alerts a message, the function returns false, and the form will not be submitted:

The function above could be called when a form is submitted:

E-mail Validation

The function below checks if the content has the general syntax of an email.

This means that the input data must contain an @ sign and at least one dot (.). Also, the @ must not be the first character of the email address, and the last dot must be present after the @ sign, and minimum 2 characters before the end:

The function above could be called when a form is submitted:

What is a Cookie?

A cookie is a variable that is stored on the visitor’s computer. Each time the same computer requests a page with a browser, it will send the cookie too. With JavaScript, you can both create and retrieve cookie values.

Examples of cookies:

• Name cookie – The first time a visitor arrives to your web page, he or she must fill in her/his name. The name is then stored in a cookie. Next time the visitor arrives at your page, he or she could get a welcome message like “Welcome John Doe!” The name is retrieved from the stored cookie
• Password cookie – The first time a visitor arrives to your web page, he or she must fill in a password. The password is then stored in a cookie. Next time the visitor arrives at your page, the password is retrieved from the cookie
• Date cookie – The first time a visitor arrives to your web page, the current date is stored in a cookie. Next time the visitor arrives at your page, he or she could get a message like “Your last visit was on Tuesday August 11, 2005!” The date is retrieved from the stored cookie

Create and Store a Cookie

In this example we will create a cookie that stores the name of a visitor. The first time a visitor arrives to the web page, he or she will be asked to  fill in her/his name. The name is then stored in a cookie. The next time the visitor arrives at the same page, he or she will get welcome message.

First, we create a function that stores the name of the visitor in a cookie variable:

The parameters of the function above hold the name of the cookie, the value of the cookie, and the number of days until the cookie expires.

In the function above we first convert the number of days to a valid date, then we add the number of days until the cookie should expire. After that we store the cookie name, cookie value and the expiration date in the document.cookie object.

Then, we create another function that returns a specified cookie:

The function above makes an array to retrieve cookie names and values, then it checks if the specified cookie exists, and returns the cookie value.

Last, we create the function that displays a welcome message if the cookie is set, and if the cookie is not set it will display a prompt box, asking for the name of the user, and stores the username cookie for 365 days, by calling the setCookie function:

All together now:

The example above runs the checkCookie() function when the page loads.

source from: w3schools