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Teach yourself javascript pdf

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Sams Teach Yourself JavaScript™ in 24 Hours, Fifth Edition. Copyright © by Pearson PDF files, JavaScript support in, percent sign (%), JavaScript in 24 Hours, Sams Teach Yourself, subiecte.info - Ebook download as PDF File .pdf), Text File .txt) or read book online. The illustrations are contributed by various artists: Cover and chapter illus- trations by Madalina Tantareanu. Pixel art in Chapters 7 and 16 by Antonio. Perdomo.


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Sams Teach Yourself. JavaScript® in 24 Hours. Sixth Edition. Phil Ballard. East 96th Street, Indianapolis, Indiana, USA. Teach Yourself JavaScript in 21 Days East 96th St., Indianapolis, Indiana, USA ™ Sams Teach Yourself JavaScript™ in 21 Days ACQUISITIONS. th Street, Indianapolis, Indiana, USA in Hours. Michael Moncur. JavaScript. Teach. Yourself. Teach. Yourself.

Tip In practice. Notice that the line of text inside the parentheses is contained within quotation marks. Instead of using new Object. Click here to view code image if input. Strings A string is a sequence of characters from within a given character set for example. Note the break statement after each case. As with new nodes created by createElement and createTextNode.

Note JavaScript is an interpreted language. This offers big advantages in that JavaScript programs are easy to read.. Each time your browser is asked to load and display a page.

Internet Explorer is shipping in version As part of this parsing process. In the early days. Since then. Netscape Navigator has been reborn as Mozilla Firefox currently in version As well as DOM Level 0. JavaScript provided rather primitive access to certain parts of a web page. We discuss how to include JavaScript in your pages in much more detail in Hour 2.

Note In this book. It is this model that the browser then refers to when rendering the visible page. The examples in this hour place their JavaScript code within the body section of the document.

Javascript teach pdf yourself

JavaScript programs could gain access. You are recommended to upgrade your browser to the latest stable version. Right at the top of the hierarchical tree is the browser window object. Each object also has a list of properties that describe it.

Google Chrome. This book concentrates on more modern browsers that are compatible with DOM Level 1 or better. The situation has improved markedly for web developers. Apart from a few irritating quirks. All of this information is accessible via JavaScript as a parentchild hierarchy of objects.

The window object has various child objects. Any HTML page loaded into the browser creates a document object containing all of the HTML and other resources that go into making up the displayed page.

All of these offer excellent support for the DOM. Apple Safari. The first child object shown in Figure 1. Note The use of early browsers such as Netscape Navigator any version and Internet Explorer up to version 5. The window and document Objects Each time your browser loads and displays a page.

These objects. In the DOM. This object is a parent or ancestor to everything else in the DOM representation of your page. We look in detail at these objects in Hour 4. We can simply use window.. For example object1. Object Notation The notation we use to represent objects within the tree uses the dot or period: Tip The window object always contains the current browser window. As a shortcut.

We begin with two methods. The window object. Here we are calling the alert method of the window object. If you have several windows open. Tip In practice. To refer to one of these documents. When you call the alert method. So Click here to view code image. Notice that the line of text inside the parentheses is contained within quotation marks.

Tip Until the user clicks OK. The appearance of the dialog changes in detail depending on the particular browser. This line of code. These can be single or double quotes. Try it Yourself: This method. By the time you come to write more advanced JavaScript programs. A dialog that behaves this way is known as a modal dialog. If your browser does this. If you have more than one browser installed on your computer. You should see a display similar to Figure 1.

Caution The default security settings in some browsers cause them to show a security warning when they are asked to open local content. Caution Some text editor programs might try to add a. Save it to a convenient place on your computer.

JavaScript in 24 Hours, Sams Teach Yourself, 6th Edition - IT电子书

Be sure your saved file has the extension. Reading a Property of the document Object.. Notice that document. The result is shown in Figure 1. Without the quote marks. Edit hello. You had an overview of the sorts of things JavaScript can do to enhance your web pages and improve the experience for your users. In the lessons that follow.

You may recall from earlier in the hour that objects in the DOM tree have properties and methods. JavaScript sends to the alert method the value contained in the document.

Most definitely. Neither d. A compiled language b.

Javascript pdf yourself teach

An interpreted language c. The document object. The document method c. Quiz 1. Other than in extreme circumstances.

Is JavaScript a compiled or an interpreted language? The top level of the DOM hierarchy is occupied by: Both 2. How many different browsers should I test in? The document property b. If you have a particularly large piece of JavaScript code. As many as you practically can. Writing standards-compliant code that avoids browser-specific features will go a long way toward making your code run smoothly in different browsers.

In fact. Be careful—property names are case sensitive. The window object is at the top of the DOM tree. The window object Answers 1. Note the capital M. The program code is written in plain text. JavaScript is an interpreted language.

Try the example code from this hour in as many different browsers as you have access to. See whether you can then modify the code to use document. What differences do you note in how the example pages are displayed? Try rewriting that script to instead output the document. Javascript statements are written here.

Various ways to include JavaScript in your web pages The basic syntax of JavaScript statements How to declare and use variables Using mathematical operators How to comment your code Capturing mouse events You learned in Hour 1. Including JavaScript in Your Web Page In the previous hour I said that JavaScript programs are passed to the browser along with page content—but how do we achieve that?

If your JavaScript file is not in the same folder as the calling script In this hour you learn more about how JavaScript can be added to your web page. Hour 2. Just include the raw JavaScript code. Note It is customary to give files of JavaScript code the file extension.

This is particularly important in the context of JavaScript libraries. Performance is slightly improved because your browser caches the included file. When the JavaScript code is updated. You learn about functions in Hour 3. Listing 2. The code for the HTML page is kept cleaner.

JavaScript Statements JavaScript programs are lists of individual instructions that we refer to as statements. To interpret statements correctly.. Unless you have a reason to support very old browsers.

After the code has been read and executed. A comment written using this syntax can span multiple lines: To ease the readability of your code. Click here to view code image this is statement 1. We refer to such lines as comments. To add a multiline comment in this way. A comment that occupies just a single line of code can be written by placing a double forward slash before the content of the line: Comments can act as reminders to you.

Many coders of JavaScript. We can set the value stored in netPrice with a simple statement: In CamelCase. Our variables can be called pretty much anything we want. We call this assigning a value to the variable. Generally the difference is so small as to be barely noticeable. In this example. Such data can take many different forms—an integer or decimal number. JavaScript allows us to carry out operations using the standard arithmetic operators of addition.

Having variable names such as productName and netPrice makes code much easier to read and maintain than if the same variables were called var and myothervar Alternatively we can combine these two statements conveniently and readably into one: We could then. The generated dialog would evaluate the variable and display it this time. Arithmetic Operations First. To assign a character string as the value of a variable. We can use JavaScript to subtract -. To calculate the remainder from a division.

We can use variable names in our operations too: Tip If you need to increment or decrement a variable by a value other than one.

For example. We can use this notation for other arithmetic operators. JavaScript uses precedence rules to determine in what order the calculation should be done. The following two lines of code are equivalent: To calculate the average correctly. So are these two: If you have doubts about the precedence rules. I would recommend that you always use parentheses liberally. You can find detailed information on JavaScript precedence at http: There is no cost to doing so.

JavaScript converts the numeric value to a string and concatenates the two: Figure 2. Convert Celsius to Fahrenheit To convert a temperature in degrees Celsius to one measured in degrees Fahrenheit.

You should get the result shown in Figure 2. To achieve this. It serves us well for the examples in Part I of this book.. Capturing Mouse Events One of the fundamental purposes of JavaScript is to help make your web pages more interactive for the user. We are going to investigate three of these: One way we can implement it is to add one more attribute to the HTML element: All of these occurrences we refer to as events.

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JavaScript deals with events by using so-called event handlers. Click here to view code image alert 'You clicked the button! In this case. The value given to the onclick attribute is the JavaScript code we want to run when the HTML element in this case a button is clicked. When the user clicks on the button. This convention has arisen because. Replacing onmouseover with onmouseout in the code will. The onMouseOut event. When using this within an event handler added via an attribute of an HTML element.

Creating an Image Rollover We can use the onMouseOver and onMouseOut events to change how an image appears while the mouse pointer is above it. The code is shown in Listing 2. You can change the image names tick. You should see that the image changes as the mouse pointer enters. In this example we used two images.

Save the HTML file and open it in your browser. Summary You covered quite a lot of ground this hour. You studied how to declare variables in JavaScript, assign values to those variables, and manipulate them using arithmetic operators. Does it matter? Empty spaces, such as the space character, tabs, and blank lines, are completely ignored by JavaScript. You can use such blank space, which programmers usually.

What is an onClick event handler? A script that executes in response to the user clicking the mouse c. An HTML element that the user can click 2. None b. Exactly one c. Any number 3. Which of these is NOT a true statement about variables? Their names are case sensitive. They can contain numeric or non-numeric information. Their names may contain spaces. Answers 1. An onClick event handler is a script that executes when the user clicks the mouse. Variable names in JavaScript must not contain spaces.

Exercises Starting with Listing 2. Instead, add an onClick handler to set the.

JavaScript in 24 Hours, Sams Teach Yourself, 6e.pdf

You can access the image title using this. Can you think of an easy way to test whether your script has correctly set the new image title? Hour 3. How to define functions How to call execute functions How functions receive data Returning values from functions About the scope of variables Commonly, programs carry out the same or similar tasks repeatedly during the course of their execution. For you to avoid rewriting the same piece of code over and over again, JavaScript has the means to parcel up parts of your code into reusable modules, called functions.

Using functions also makes your code easier to debug and maintain. There may be 50 places in your code where such calculations are carried out. However, if all such calculations are wrapped up in a few functions used throughout the application, then you just need to make changes to those functions. Your changes will automatically be applied all through the application.

Functions are one of the basic building blocks of JavaScript and will appear in virtually every script you write. In this hour you see how to create and use functions. General Syntax Creating a function is similar to creating a new JavaScript command that you can use in your script.

Inside the braces go the. JavaScript statements that make up the function. In the case of the preceding example, we simply have one line of code to pop up an alert dialog, but you can add as many lines of code as are necessary to make the function Caution The keyword function must always be used in lowercase, or an error will be generated. Calling Functions Code wrapped up in a function definition will not be executed when the page loads. Instead, it waits quietly until the function is called.

To call a function, you simply use the function name with the parentheses wherever you want to execute the statements contained in the function: For example, you may want to add a call to your new function sayHello to the onClick event of a button: Tip Function names, like variable names, are case-sensitive. A function called MyFunc is different from another called myFunc. JavaScript objects, such as document.

Listing 3. The result of clicking the button is shown in Figure 3. Passing Arguments to Functions It would be rather limiting if your functions could only behave in an identical fashion each and every time they were called, as would be the case in the preceding example. Fortunately, you can extend the capabilities of functions a great deal by passing data to them. You do this when the function is called, by passing to it one or more arguments: Now we can call our function, replacing the variable x with a number.

Calling the function like the following results in a dialog box being displayed that contains the result of the calculation, in this case Of course, you could equally pass a variable name as an argument. The following code would also generate a dialog containing the number Multiple Arguments Functions are not limited to a single argument. When you want to send multiple arguments to a function, all you need to do is separate them with commas: You can use as many arguments as you want.

Caution Make sure that your function calls contain enough argument values to match the arguments specified in the function definition. If any of the arguments in the definition are left without a value, JavaScript may issue an error, or the function may perform incorrectly.

If your function call is issued with too many arguments, the extra ones will be ignored by JavaScript. The variable names in the argument list act like placeholders for the actual values that will be passed when the function is called.

The names that you give to arguments are only used inside the function definition to specify how it works. We talk about this in more detail later in the hour when we discuss variable scope. The function buttonReport takes three arguments, those being the id, name, and value of the button element that has been clicked. With each of these three pieces of information, a short message is constructed.

These three messages are then concatenated into a single string, which is passed to the alert method to pop open a dialog containing the information. Such a prefixed character is known as an escape sequence. We need to add an onClick event handler to this button from which to call our function. The complete listing is shown in Listing 3. Use your editor to create the file buttons. You should find that it generates output messages like the one shown in Figure 3.

JavaScript in 24 Hours, Sams Teach Yourself, Sixth Edition

Returning Values from Functions OK, now you know how to pass information to functions so that they can act on that information for you.

But how can you get information back from your function? Luckily, there is a mechanism to collect data from a function call—the return value.

Instead of using an alert dialog within the function, as in the previous example, this time we prefixed our required result with the return keyword. To access this value from outside the function, we simply assign to a variable the value returned by the function: Note The values returned by functions are not restricted to numerical quantities as in this example.

In fact, functions can return values having any of the data types supported by JavaScript. We discuss data types in Hour 5.

Yourself pdf teach javascript

Tip Where a function returns a value, we can use the function call to pass the return value directly to another statement in our code. The value of 27 returned from the function call cube 3 immediately becomes the argument passed to the alert method. Scope of Variables We have already seen how to declare variables with the var keyword.

There is a golden rule to remember when using functions: If we run this code, we first see an alert dialog with the value of the variable invoiceValue which should be 55, but in fact will probably be something like We will not, however, then see an alert dialog containing the value of the variable total.

Instead, JavaScript simply produces an error. Whether you see this error reported depends on your browser settings—you learn more about error handling later in the book—but JavaScript will be unable to display an alert dialog with the value of your variable total.

This is because we placed the declaration of the variable total inside the addTax function. We used the return keyword to pass back just the value stored in the variable total, and that value we then stored in another variable, invoice. We refer to variables declared inside a function definition as being local variables; that is, local to that function. Variables declared outside any function are known as global variables.

To add a little more confusion, local and global variables can have the same name, but still be different variables! The range of situations where a variable is defined is known as the scope of the variable—we can refer to a variable as having local scope or global scope.

Within the showVars function we manipulate two variables, a and b. The variable a we define inside the function; this is a local variable that only exists inside the function, quite separate from the global variable also called a that we declare at the very beginning of the script. The variable b is not declared inside the function, but outside; it is a global variable.

When the page is loaded, showVars returns a message string containing information about the updated values of the two variables a and b, as they exist inside the function—a with local scope, and b with global scope.

A message about the current value of the other, global variable a is then appended to the message, and the message displayed to the user. Copy the code into the file scope. Compare your results with Figure 3. Summary In this hour you learned about what functions are, and how to create them in JavaScript. You learned how to call functions from within your code, and pass information to those functions in the form of arguments. You also found out how to return information from a function to its calling statement.

Finally, you learned about the local or global scope of a variable, and how the scope of variables affects how functions work with them. Can one function contain a call to another function? Most definitely; in fact, such calls can be nested as deeply as you need them to be. What characters can I use in function names? Function names must start with a letter or an underscore and can contain letters, digits, and underscores in any combination.

They cannot contain spaces, punctuation, or other special characters. Functions are called using a. The function keyword b.

Sams Teach Yourself JavaScript in 24 Hours (4th Edition)

The call command c. The function name, with parentheses 2. What happens when a function executes a return statement?

Pdf teach yourself javascript

An error message is generated. A value is returned and function execution continues. A value is returned and function execution stops. A variable declared inside a function definition is called a. A local variable b. A global variable c. An argument.

A function is called using the function name. After executing a return statement, a function returns a value and then ceases function execution. Exercises Write a function to take a temperature value in Celsius as an argument, and return the equivalent temperature in Fahrenheit, basing it on the code from Hour 2.

Test your function in an HTML page. Hour 4. We also looked at one of its child objects, document. In this hour, we introduce some more of the utility objects and methods that you can use in your scripts.

Interacting with the User Among the methods belonging to the window object, there are some designed specifically to help your page communicate with the user by assisting with the input and output of information. The term modal means that script execution pauses, and all user interaction with the page is suspended, until the user clears the dialog.

The alert method takes a message string as its argument: The confirm dialog, though, provides the user with a. Clicking on either button clears the dialog and allows the calling script to continue, but the confirm method returns a different value depending on which button was clicked—Boolean true in the case of OK, or false in the case of Cancel.

Note that here, though, we pass the returned value of true or false to a variable so we can later test its value and have our script take appropriate action depending on the result. In this case, though, the dialog invites the user to enter information. A prompt dialog is called in just the same manner as confirm: The prompt method also allows for an optional second argument, giving a default response in case the user clicks OK without typing anything: If the user clicks OK or presses Enter without typing anything into the prompt dialog.

The return value from a prompt dialog depends on what option the user takes: If the user types in input and clicks OK or presses Enter. If the user dismisses the dialog that is. When treated as a number it takes the value 0. Click here to view code image. Note The null value is used by JavaScript on certain occasions to denote an empty value. For now.

The prompt dialog generated by the previous code snippet is shown in Figure 4. Imagine your HTML contains the following element: Content of DIV element. The variable myDivContents will now contain the string value: Click here to view code image document.

We now have access to the chosen page element and all of its properties and methods. Caution Of course. Its methods enable you to use the list.

Click here to view code image history. We can think of the page URL as a series of parts: This can be an integer. You can use this property to find how many pages the user has visited: Computer Science. Electronic Engineering. Linux and Unix. Microsoft and. Mobile Computing. Networking and Communications.

Software Engineering. Special Topics. Web Programming. Who This Book Is For Those who have at least a basic understanding of HTML and web page design in general and want to move on to adding some extra interactivity to your pages. Those who currently code in another programming language and want to see what additional capabilities JavaScript can add to your armory Someone who has never done any computer programming.

First Steps with JavaScript Hour 1. Cooking with Code Hour 5. Objects Hour 8. Using JavaScript Libraries Hour Using Libraries Why Use a Library? Advanced Topics Hour Limitations of Cookies The document.