Java. Script Quick Guide. Java. Script - Quick Guide. Java. Script - Overview. What is Java. Script ? Javascript is a dynamic computer programming language. It is lightweight and most commonly used as a part of web pages, whose implementations allow client- side script to interact with the user and make dynamic pages. It is an interpreted programming language with object- oriented capabilities. Java. Script was first known as Live. Script, but Netscape changed its name to Java. Script, possibly because of the excitement being generated by Java. Java. Script made its first appearance in Netscape 2. Live. Script. The general- purpose core of the language has been embedded in Netscape, Internet Explorer, and other web browsers. The ECMA- 2. 62 Specification defined a standard version of the core Java. Script language. Java. Script is a lightweight, interpreted programming language. Designed for creating network- centric applications. Complementary to and integrated with Java. Complementary to and integrated with HTML. Open and cross- platform. Client- side Java. Script. Client- side Java. Script is the most common form of the language. The script should be included in or referenced by an HTML document for the code to be interpreted by the browser. It means that a web page need not be a static HTML, but can include programs that interact with the user, control the browser, and dynamically create HTML content. The Java. Script client- side mechanism provides many advantages over traditional CGI server- side scripts. For example, you might use Java. Script to check if the user has entered a valid e- mail address in a form field. Steps to Disable Back Button in Browser using JavaScript. Disable Back Button in Browser using JavaScript. Back Button Disable. There are three primary means by which most Hubbers build a strong readership on HubPages: They publish in-depth, high quality, search-friendly articles on subjects. How can I close a browser window without receiving the Do you want to close this window prompt? The prompt occurs when I use the window.close(); function. Variable types are not important in JavaScript. They may be interchanged as necessary. This means that if a variable is a string one minute, it can be an. An experimental microcontent WikiWikiWeb built by Jeremy Ruston. It's written in HTML and JavaScript to run on any browser without needing any serverside logic. This tutorial shows how to create items on your page using JavaScript that you can drag and drop. Even if you regularly eschew meat-eating and take public transportation, all your efforts at reducing your carbon footprint can be easily outweighed by indulging in. The Java. Script code is executed when the user submits the form, and only if all the entries are valid, they would be submitted to the Web Server. Java. Script can be used to trap user- initiated events such as button clicks, link navigation, and other actions that the user initiates explicitly or implicitly. Advantages of Java. Script. The merits of using Java. Script are . This saves server traffic, which means less load on your server. Immediate feedback to the visitors . It lacks the following important features . This has been kept for security reason. Java. Script cannot be used for networking applications because there is no such support available. Java. Script doesn't have any multithreading or multiprocessor capabilities. Once again, Java. Script is a lightweight, interpreted programming language that allows you to build interactivity into otherwise static HTML pages. Java. Script Development Tools. One of major strengths of Java. Script is that it does not require expensive development tools. You can start with a simple text editor such as Notepad. Since it is an interpreted language inside the context of a web browser, you don't even need to buy a compiler. To make our life simpler, various vendors have come up with very nice Java. Script editing tools. Some of them are listed here . Front. Page also provides web developers with a number of Java. Script tools to assist in the creation of interactive websites. Macromedia Dreamweaver MX . It provides several handy prebuilt Java. Script components, integrates well with databases, and conforms to new standards such as XHTML and XML. Macromedia Home. Site 5 . Java. Script 2. 0 conforms to Edition 5 of the ECMAScript standard, and the difference between the two is extremely minor. The specification for Java. Script 2. 0 can be found on the following site: http: //www. Today, Netscape's Java. Script and Microsoft's JScript conform to the ECMAScript standard, although both the languages still support the features that are not a part of the standard. Java. Script - Syntax. Java. Script can be implemented using Java. Script statements that are placed within the < script>.. A simple syntax of your Java. Script will appear as follows. Typically, its value will be javascript. Although recent versions of HTML (and XHTML, its successor) have phased out the use of this attribute. Type . We added an optional HTML comment that surrounds our Java. Script code. This is to save our code from a browser that does not support Java. Script. The comment ends with a . Next, we call a function document. HTML document. This function can be used to write text, HTML, or both. Take a look at the following code. You can use spaces, tabs, and newlines freely in your program and you are free to format and indent your programs in a neat and consistent way that makes the code easy to read and understand. Semicolons are Optional. Simple statements in Java. Script are generally followed by a semicolon character, just as they are in C, C++, and Java. Java. Script, however, allows you to omit this semicolon if each of your statements are placed on a separate line. For example, the following code could be written without semicolons. This means that the language keywords, variables, function names, and any other identifiers must always be typed with a consistent capitalization of letters. So the identifiers Time and TIME will convey different meanings in Java. Script. NOTE . This may span multiple lines. Java. Script also recognizes the HTML comment opening sequence < !- -. Java. Script treats this as a single- line comment, just as it does the // comment. The HTML comment closing sequence - -> is not recognized by Java. Script so it should be written as //- ->. Example. The following example shows how to use comments in Java. Script. It is similar to comments in C++. This is a multiline comment in Java. Script. * It is very similar to comments in C Programming. Enabling Java. Script in Browsers. All the modern browsers come with built- in support for Java. Script. Frequently, you may need to enable or disable this support manually. This chapter explains the procedure of enabling and disabling Java. Script support in your browsers: Internet Explorer, Firefox, chrome, and Opera. Java. Script in Internet Explorer. Here are simple steps to turn on or turn off Java. Script in your Internet Explorer . Select I’ll be careful, I promise! Then you will find the list of configure options in the browser. In the search bar, type javascript. There you will find the option to enable or disable javascript by right- clicking on the value of that option . If javascript is disabled; it gets enabled upon clicking toggle. Java. Script in Chrome. Here are the steps to turn on or turn off Java. Script in Chrome . However the most preferred ways to include Java. Script in an HTML file are as follows . In this case, you would not have any function defined using Java. Script. Take a look at the following code. The script tag provides a mechanism to allow you to store Java. Script in an external file and then include it into your HTML files. Here is an example to show how you can include an external Java. Script file in your HTML code using script tag and its src attribute. These are the type of values that can be represented and manipulated in a programming language. Java. Script allows you to work with three primitive data types . Strings of text e. In addition to these primitive data types, Java. Script supports a composite data type known as object. We will cover objects in detail in a separate chapter. Note . All numbers in Java. Script are represented as floating- point values. Java. Script represents numbers using the 6. IEEE 7. 54 standard. Java. Script Variables. Like many other programming languages, Java. Script has variables. Variables can be thought of as named containers. You can place data into these containers and then refer to the data simply by naming the container. Before you use a variable in a Java. Script program, you must declare it. Variables are declared with the var keyword as follows. You can do variable initialization at the time of variable creation or at a later point in time when you need that variable. For instance, you might create a variable named money and assign the value 2. For another variable, you can assign a value at the time of initialization as follows. You should not re- declare same variable twice. Java. Script is untyped language. This means that a Java. Script variable can hold a value of any data type. Unlike many other languages, you don't have to tell Java. Script during variable declaration what type of value the variable will hold. The value type of a variable can change during the execution of a program and Java. Script takes care of it automatically. Java. Script Variable Scope. The scope of a variable is the region of your program in which it is defined. Java. Script variables have only two scopes. Global Variables . Function parameters are always local to that function. Within the body of a function, a local variable takes precedence over a global variable with the same name. If you declare a local variable or function parameter with the same name as a global variable, you effectively hide the global variable. Take a look into the following example. These keywords are mentioned in the next section. For example, break or boolean variable names are not valid. Java. Script variable names should not start with a numeral (0- 9). They must begin with a letter or an underscore character. For example, 1. 23test is an invalid variable name but . For example, Name and name are two different variables. Java. Script Reserved Words. A list of all the reserved words in Java. Script are given in the following table. They cannot be used as Java. Script variables, functions, methods, loop labels, or any object names. Java. Script - Operators. What is an operator? Let us take a simple expression 4 + 5 is equal to 9. Here 4 and 5 are called operands and . Java. Script supports the following types of operators. Arithmetic Operators. Comparision Operators. Logical (or Relational) Operators. Assignment Operators. Conditional (or ternary) Operators. Lets have a look on all operators one by one. Arithmetic Operators. Java. Script supports the following arithmetic operators . If a condition is true, then the Logical NOT operator will make it false. Java. Script tutorial. Table of contents. Important guidelines. First let's learn some important stuff. There are lots of browsers out there that cannot. Java. Script. Although browsers generally support more and more with each release. Java. Script. language available for browsers to support. No browser will ever support all of it, and you. There are many reasons why people cannot or will not 'upgrade' to your chosen browser. If your site. uses Java. Script for navigation or content, then that navigation and content should be there without Java. Script enabled. If you want to use a script in. There are also many browsers out there that you do not realise exist. I know of well over a hundred. Java. Script to varying degrees. If your script uses something. There is no magic formula for this, but the basic rules are that you should not detect a. You will get it wrong, and you will mistakenly detect one. You will. make incorrect assumptions about current and future browsers, and you will cause problems for. This tutorial should help you learn how to correctly detect capabilities, and. When there are different ways to do the. Introduction to Java. Script. Java. Script is a programming language that can be included on web pages to make them more. You can use it to check or modify the contents of forms, change images, open new. You can even use it with CSS to make DHTML (Dynamic. Hyper. Text Markup Language). This allows you to make parts of your web pages appear or disappear. Java. Scripts only execute on the page(s) that are on your browser. When the user stops viewing that page, any scripts that were running on. The only exceptions are cookies or various client side storage APIs, which can be used by many pages. Before we go any further, let me say; Java. Script has nothing to do with Java. If we are honest. Java. Script, originally nicknamed Live. Wire and then Live. Script when it was created by Netscape, should in fact be. ECMAscript as it was renamed when Netscape passed it to the ECMA for standardisation. Java. Script is a client side, interpreted, object oriented, high level scripting language, while Java is a. Now after that mouthful, here's what it means. Client side. Programs are passed to the computer that the browser is on, and that computer runs them. Examples of this would be PHP, Perl, ASP, JSP etc. Interpreted. The program is passed as source code with all the programming language visible. It is. then converted into machine code as it is being used. Compiled languages are converted into machine code first. Java is actually dual half compiled. Although they may be complete programming. They often. do not create their own user interfaces, and instead will rely on the other programs to create an interface. This is quite accurate for Java. Script. We do not have to tell the browser exactly what to put on the. API known as canvas that makes this possible if needed). The browser. will also take care of the memory management and thread management, leaving Java. Script free to get on with the. High level. Written in words that are as close to english as possible. The contrast would be with assembly code, where. Object oriented. See the section on 'object oriented programming' for details. How is Java. Script constructed. The basic part of a script is a variable, literal or object. A variable is a word that. Operators assign literal values. The next most important part of a script is a control structure. Control structures say what. Functions collect control structures, actions and assignments together and can be told to run. The most obvious parts of a script are the actions it performs. Some of these are done with. Methods are a special kind of function and may do. Events can be used to detect actions, usually created by the user, such as moving or clicking. When triggered, events can be used to run functions. Lastly and not quite so obvious is referencing. This is about working out what to write to. As an example, think of the following situation. A person clicks a submit button on a form. So, we tell the form to detect the submit event. The function contains a control structure that uses a comparison operator to test the. Of course we have to work out how to reference the text. The text box is an object. One of the variables it holds is the text that is written. The text written in it is a literal. If the text box is not empty, a method is. Examples. All examples on this page and elsewhere in my Java. Script tutorial are provided free of charge. I will leave that to your own creativity. Note that the syntax highlighted source of all the header files I use in these examples, as well as. Java. Script libraries page. The header files. The header file scripts are meant to be real scripts for real use, not tutorials. I have included them. I agree. that they are not always easy to read, but that is mainly because they are optimised for real use. You may. choose to see this as a bad programming method, but I do not, as I can always see what I was intending for. To give you an example of a more 'friendly' format, which is easier to use as a learning aid, one of my. Non DHTMLThe most popular use of Java. Script; changing images when the mouse hangs over a link. The next most popular use of Java. Script; opening new browser windows. The next most popular use of Java. Script; writing dynamic content. The next most popular use of Java. Script; checking forms. Slightly less used but just as useful, retaining variables from one page for use on another page. Some specialist scripts. The most irresponsible script. Browser sniffing - to be used only to help avoid browser specific bugs, not to determine capability. DHTMLAppearing / disappearing content. Movable content. Rewritable document content. W3. C DOMThese scripts any many more are included on my Java. Script libraries page. These games require various different technologies like HTML, CSS, DHTML, etc. Not all browsers will be able. D games, because they are demanding on resources. The simpler games may. Netscape 3. These games are all on my games site. Adding Java. Script to a page. You can add a script anywhere inside the head or body sections of your document. However, to keep your document well structured there are some basic guidelines: Most scripts can go inside the document head. This keeps them out of the way of the main document content. If your script needs to run at a certain stage during page layout (for example, if it uses document. If the script is very small, then put it all where it will be used. If it is larger, then put it inside the head inside a function, and you can then call that function when you need it. If your script is used on more than one page, or if it is of any significant size, then put it in its own file, and load it in the document head. Not only will this help to keep the clutter of the document, but it will also help avoid potential syntax problems (I will cover these later). As an extra benefit, these can be used by multiple pages, allowing browsers to use their cache, and saving bandwidth for you and your visitors. Adding a script to the page. To insert Java. Script into a web page, use the < script> tag. You should use the type attribute to specify the type of script being used, which in the case of Java. Script is text/javascript. It is also possible to the language attribute to say what Java. Script version you are using. In practice, this number means very little to browsers. They may claim to support a specific version, but will have vastly different capabilities. All Java. Script supporting browsers currently in use will support a level of Java. Script equivalent to Java. Script 1. 2 (represented as . Since the language is so unreliable, you should generally omit this attribute, although it is common to see scripts using it. Your script can then detect if the browser is capable of running your script, and it can do this a lot more accurately than the version number can. This is an example of a script tag, used to include a script in your page: < script type=. The double slash indicates a single line comment. Everything after it on the same line will be ignored by the script engine. The slash- asterisk indicates a block comment. Everything after it will be ignored by the script engine until an asterisk- slash is encountered.< script type=. In reality, this is only for very old browsers that are not used at all any more, so there is no need for anything to be put there. Scripts in header files are executed as if they were in the main page. If the script referances any external files, such as images, the addresses it uses are relative to the main page, not the script URI. Commenting out your scripts. This is not needed any more. All current browsers are aware of script tags, and how to treat their contents, since they have been part of HTML since HTML 3. Browsers that do not understand HTML 3 or scripts (these are virtually never used now) will display the script as if it was the content of the page. You can hide the script from them by commenting out your script with standard HTML comments. Browsers that understand script will simply ignore these comments, and will just interpret the script within them. The opening comment is ignored as if it were a normal single line Java. Script comment. The closing comment will not, so it needs to have a Java. Script comment put before it: < script type=. Script tags are not treated as being special. Their contents are treated. XHTML, so various operators can be misinterpreted as part of the markup. To avoid this. it is best to put all scripts in external script files so that they do not interfere with the page itself. If you feel the need to put something directly on the page, you can declare it as CDATA (the default for script contents in normal HTML): < script type=. Again, this really is not needed, since browsers that do not understand script also do not understand XHTML, but in case you want to use it (maybe you are serving it as XHTML to some browsers, and HTML to others), this is what to use: < script type=.
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