What are they used for in javascript? How to enable JavaScript in Google Chrome
Java Script made easy. Part 1
Scenario Java language Script is a scripting language developed by Netscape. huge opportunities for developing Internet applications running on both the client and server sides. The language is very simple, and to work with it you just need to have the concept HTML basics. JavaScript has a lot interesting features, and one of them is the ability to process not only data, but also events. An event is defined as some action performed in the context of the browser - for example, a mouse click or a page load. In addition, JavaScript integrates perfectly with PHP and complements it with the implementation of those functions that are impossible or labor-intensive to implement in PHP.
First steps in programming in JavaScript
Code JavaScript script(hereinafter referred to as JS) is placed directly in the HTML code. JS has a tag tag. Everything between the and tags is interpreted as code in that language. One of the most important commands used in JS programming is document.write(), which is needed in order to write something in the current document. In order not to be unfounded, I will give simplest example:
document.write("JavaScript is easy!!!")
Type this text in Notepad and save it with HTML extension. The result of executing this code will be the text “JavaScript is easy!!!” displayed in the browser window. You will say: “Maybe it will, but maybe it won’t,” and you will be right. If your browser does not support JS output, you will see full code instead of text. You can avoid displaying the code in such browsers by using the comment tag from HTML -
Another very important part programming in the JS language are events and event handlers. Events are mainly triggered by certain user actions. Each action describes a different type of event. Let's say that when you press the mouse button, an event called "Click" occurs; when the mouse pointer crosses any hypertext link, the MouseOver event occurs. In order for the program to react to these events, we use special programs event processing. For example, a program that handles the mouse button event is called onClick and tells the computer what to do if it happens. this event. For clarity, let's create a simple example again. Let's create a form that will contain a button, when clicked, a drop-down window will appear.
test page
Clicking the Test Button brings up a window with the text “Test completed!” (Fig. 1). Let's look at each command in this code in detail.
Using the command, we create a form with a button. The onClick="alert("Test passed!")" attribute defines what happens when the mouse button is clicked. Thus, if there is Click event, the computer will call alert("Test completed!"). The alert() function creates pop-up windows. When calling it, you need to specify a certain string in parentheses, which will appear in the drop-down window. As you can see in the code, the alert() construct uses single quotes. This is explained by the fact that in most cases it is possible to use both types of quotation marks. Moreover, it does not matter in what order they are used: first double, and then single, or vice versa. In our example, double quotes are used first, and then single quotes, and if we used the construction of two double quotes-onClick="alert("Test completed!")", then the computer would not be able to understand the script, since it is unclear which part of the structure the processing function relates to onClick events, and to which - not.
So, the window contains the text that was passed to the JS alert function. This limitation is applied for security reasons. A drop-down window can also be created using the prompt() method (see Fig. 2), but in this case the window will reproduce the text entered by the user, and therefore the script written by an “evil hacker” can take the form system message and ask you to enter a certain password. In our case, it is clear that the window was created by the browser, and not operating system, and you can’t just pick it up and delete it.
Very convenient means in JS are functions that in most cases are used as a way to chain multiple commands together. As clear example Let's say that you need to repeat some sequence many times text strings. Using the JS knowledge we already have, we could use the document.write command and get code like this:
");
");
document.write("Most interactive page
");
document.write("Java Script made easy
");
document.write("Most interactive page
");
document.write("Java Script made easy
");
// -->
The naked eye can see that the structure was built irrationally. Let's rebuild this code using the function:
All script commands that are inside curly braces, belong to the FreeFunc() function we created. Now both document.write() commands are linked and can be executed when the specified function is called. Next, we call FreeFunc() three times immediately after defining the function itself. This will cause the function to be executed three times, i.e. Both lines will be printed three times. The kicker is that the ability to pass variables when calling a function gives scripts real flexibility. Functions can also be used in conjunction with event handling procedures. For example, you can create a function calc() that will have two variables x and y, and the result of the mathematical operation will be stored in the result variable. The last command of the function will be alert(result). Next, the calc() function can be called when the button is clicked with the onClick="calc()" command, resulting in a pop-up window with the calculation result.
Working with Windows
Another feature of the JavaScript language is opening new windows in the browser. In addition, you have the opportunity to control the window creation process itself. For example, you can specify the window size, whether the new window should have a status bar, a toolbar, or a menu. The list of main parameters is given in Table 1.
Table 1. Basic parameters for creating a window in JS
Let's take a practical example of creating a new window in a browser:
As a result of executing this program, we will receive a button in the browser, when clicked, a new window with text is created (see Fig. 3).
The OpenWindow() function we created opens a new browser window. The first argument to the open() function, the empty string (""), means that in this case we do not want to specify a specific URL, and JS is obliged to create additional new document. In the script, we define the variable myWindow, with which we access the new window (it is impossible to use the window name (TestWindow) for this purpose in this case). The created window has dimensions of 300x100 pixels and has no status bar, toolbar, or menu. After opening the window, inside it we open the document object to display the text. This is done using the myWindow.document.open() command. Here we access the open() method of the document object. This command does not open a new window - it only prepares the document for upcoming printing. It is necessary to prefix document.open() with the myWindow prefix to be able to print in a new window. Further in the text of the script, using the document.write() call, the text of the new document and its parameters are formed. To do this, write regular tags into the document HTML language. In this case, you can use absolutely any tags of the hypertext language HTML markup. After finishing working with the document() command, you need to close it, for which we use the myWindow.document.close() command.
When opening a window we must use three arguments:
myWindow= open("page.htm", "TestWindow",
"width=300,height=100,status=no,toolbar=no,menubar=no");
IN in this example we specify a specific URL (page.html) and the second parameter is the window name. Knowing the name of the window, you can load a new page there using the entry
In this case, you need to specify the name of the corresponding window, and if such a window does not exist, then a new one will be created with this name. Make no mistake: the myWin variable is not the name of the window, but only with the help of this variable can you access it. The scope of this variable is limited only by the script in which it is defined. But the window name (TestWindow) is a unique identifier that can be used from any browser window. To close the window, use the close() function, and everything else is identical to working with the open() function.
Status bar
In JS, you can write to the browser status bar - all you need to do is write the desired text to windows.status. Let's look at how to use this function again with an example. Let's create a script that, when you click on a button, will display the specified text in the status bar, and when you click on the second button, erase it:
By running the program in the browser, we get a form with two buttons. When you press the On Statbar Text button, the message “The On button is pressed” appears in the status bar, and when you press the Off Statbar (Clear text) button, the status bar is cleared (see Fig. 4).
So, we have a form with two buttons, which both call the statbar() function. When the On Statbar Text key is pressed, the function is called
as follows: statbar("On button pressed"). The text in quotes is the text that we will see in the status bar. In turn, the statbar() function was declared as follows:
function statbar(txt) (
window.status = txt;)
We put (txt) in the function in parentheses. This means that the string we passed to this function is placed in the txt variable, and the txt string is written to the status bar using the command window.status = txt. Accordingly, removing text from the status bar is done by writing an empty string to window.status: (""). The uses of writing text to the status bar are limitless. You can put an explanation of the link there when you hover over it, create a ticker, or simply use it to display the date and time.
Timer
Using the timeout function, you can execute certain commands after a specified time has elapsed. I will demonstrate this in the following script:
setTimeout("alert("Welcome to the \"MyHome\" ")", 3000);
// -->
Wait 3 seconds. A window will appear
After 3 seconds of opening the page, a pop-up window will appear saying “Welcome to the MyHome page” (see Figure 5).
SetTimeout() is a method of the window object. It is designed to set a time interval. The first argument to the call is the JS code that should be executed after the specified time has elapsed (in our case, alert()). The second argument is used to indicate when this code should be executed. In this case, the time is indicated in milliseconds.
Frames
The browser window can be split into several separate frames. A frame in general terms is a rectangle-shaped field. Each frame displays the contents of its own document. Creating frames is still an HTML task, but we'll briefly cover the basics of the process in JS. Tags and are used to create frames. In the following example, we will create a script that divides the browser page into 5 frames and load a separate page into each of them:
The result of executing this script is shown in Fig. 6.
In the frame, we use the rows and cols properties and set the percentage of space occupied by frames in the browser window. The rows property means that the frames will be located on top of each other, and the cols - opposite each other. You can also set the frame size in pixels, for which it is enough not to put the % symbol after the number. In the tag we indicate a link to the page to be loaded, and with the name attribute we specify a unique name for the frame. It is possible to set the thickness of the border between frames. To do this, you need to use the border parameter in the tag and set it to some value (by default border=0). Let's look at how JavaScript "sees" the frames present in the browser window. To do this, let's turn to the window with frames we created above. JS organizes the frames presented on a web page in the form of a kind of hierarchical structure, at the top of which is the browser window. In our case, it is divided into five frames. Thus, the window as an object is the ancestor of this hierarchy, and frames are, accordingly, its descendants. We assigned unique names to these frames: frame1, frame2... frame5. Using these names, we can exchange information with the specified frames. Let's say you need to activate a certain link in the first frame, but the corresponding page should load not in the same frame, but in another one. An example of such a task would be the creation of menus or so-called navigation bars, where one frame always remains the same, but has several different links for navigation. Without delving into the study of hierarchies, let's create an example of site navigation using frames. We will create several links in one frame. When any of them is activated, the corresponding page will be placed not in the same frame, but in the adjacent one. First, let's create the frames themselves:
Next, let's create a simple HTML page "start.htm":
start page
This is the start page of our site
And the navigation bar menu:
Page 1
Page 2
Site Map
Here we see several download methods new page into the main frame. The first link uses the load() function for this purpose:
Page 1
In this line, instead of explicitly loading a new page, we invite the browser to execute a command in JavaScript - for this we use javascript parameter instead of the usual href. Next, we pass “1.htm” as an argument to the load() function, and define the load() function itself as follows:
function load(url) (
parent.main.location.href= url;)
The url is written inside the brackets. In our example, this means that the string "1.htm" is entered into the url variable when the function is called. And this new variable can now be used when working inside load() functions.
The second link uses the target parameter. This is no longer JavaScript code, but one of the HTML language constructs. We simply indicate the name of the required frame and are not required to prefix the name of the specified frame with the word parent. If you need to get rid of frames using the load() function, you only need to write parent.location.href= url in it. The result of executing our script is shown in Fig. 7.
Which of the proposed loading options to use depends on your script and the tasks it must implement.
This concludes our first acquaintance with the JavaScript language. In the following materials, we will look at predefined objects and shapes, create a clock on the page, look at working with the Image object, and also touch a little on layers and the event model.
Pavel Kuchinsky, [email protected]
JavaScript is a special type of programming language that is based on browser object representations. It is necessary in order to provide the site with greater interactivity compared to conventional static HTML documents. For example, in the interface custom type It will be possible to implement changing pictures, a creeping line from text content and much more! That's why it's important to know how to enable JavaScript in Firefox and other browsers.
JavaScript differs in that the text of software developments is embedded in HTML documents and parsed by the browsers themselves. JavaScript is a language for programming scripts on web pages.
Types of differences between JavaScript and JavaKnowing the designation of the term JavaScript, many users indiscriminately confuse this type of term with another concept - Java. Although the languages are similar due to their names, they have different types values. The main types of differences are in difficulty and in the number of advanced types of opportunities. Before you learn how to enable JavaScript browser, it is necessary to understand its characteristic features.
The implementation of "JavaScript" is more free compared to Java. For example, data type conversions occur in the simplest way. Also, the programmer will not need to compile the initial code of the software development in the JavaScript language, in other words, it is an interpreted type of language.
How does this happen in JavaScript and in Java? In JavaScript, the program processes one line after another, informing about errors is issued after each line read, if there are any. In Java, the compiler shows these types of information after reading the complete text of the software design.
Before you enable JavaScript, remember that it is not intended to be a language replacement. Java programming. It is best to use the first type of language as a complement to the second.
WITH JavaScript support it is possible to create dynamic types HTML documents. Static Views HTML pages gone into the past tense. "JavaScript" connects all the building blocks of applications into a single whole. In other words, it serves as a foundation builder, doing field checks HTML forms until they are transmitted to the server. Knowing how to enable JavaScript in Firefox and other browsers is essential for them to work correctly online.
Management software developments in this programming language go through local administrations communication data. Users have the opportunity to observe in various windows the types of warning messages that are displayed with JavaScript support.
What's happened JavaScript error and how to run JavaScriptLet's start with the fact that JavaScript makes it possible to add various interactive services to any website, safely add voting (surveys) and similar content without the risk of unnecessary page reloading. In these cases, types of scripts significantly help save user traffic and allow you to copy graphics High Quality, create types of galleries with images and do many other functions useful type. But then, in order to run types of scripts, you first need to activate them.
Next, you need to remember about the usual types of problems of network users. In recent times, there has been an increase in situations where a person, having visited his page on a social network, finds error messages at the top of the windows: “JavaScript error”, “JavaScript is not enabled”, “For correct operation JavaScript must be enabled on the site." In such cases, users have problems uploading photos and videos on the social network.
In fact, the method of running scripts is very simple, it only requires a few basic steps that even the most inexperienced users can do. Step-by-step instruction as follows:
- first you need to start personal Mozilla browser Firefox;
- after that, open the browser options, then click on the corresponding button in the form of three parallel lines next to the introduction line;
- now a huge window with many tabs has opened in front of you; the one you need is called “Content”, click on it;
- then it’s even simpler: find the line “Use JavaScript” and check the box next to it;
- Click "OK" and restart your personal browser.
At this point, the instructions on how to enable JavaScript in Firefox can be considered complete.
Disabling JavaScriptAccordingly, if the need to use JavaScript is no longer necessary, you can disable it in the same way as written above this type functions. To do this, also go to “Settings” - “Content”, uncheck the box next to “Use JavaScript”. Ready!
Also, if you have a browser Mozilla Firefox updated to latest version, then it would be good to check whether the settings have been lost after updates, as sometimes this happens. It is also worth noting that almost all types of social networks use interactive types of forms, therefore, without the included types of scripts, it will not be possible to fully view pages.
I can be unavailable messages, alerts, discussions. Sometimes failures occur, and if in social networks Some types of sections suddenly became inaccessible, but at the same time there are types of scripts activated in the browser, try turning them off and then turning them on again. Perhaps this method will solve the problem. If not, then there is always the option of resetting the options to standard. How to enable JavaScript in Internet Explorer and in other browsers? The same way.
Web scripts are programs that are written directly in html code or simply in files, which is more preferable. These programs are written in JavaScript. Thus, when talking about what Javascripts is, we can say that it is a programming language that is interpretive.
The JavaScript is read by the browser, and then the written expressions are executed and the manipulations that are specified on the page are performed. JavaScript is similar in syntax to programming languages such as Java, C++ and C.
JavaScript owes its appearance to the developments of companies such as Sun Microsystems (Oracle) and Netscape (Mozilla). The original name of the language was LiveScript. However, due to the fact that the Java language from Sun Microsystems was then very popular, Netscape's marketing department decided to change the name of the language to JavaScript. At the same time, there was an expectation that this step would add popularity to the language. Also, speaking of that, it should be noted that Java and JavaScript are two different languages.
ECMA-262 is the official standard for this language. The name of this JavaScript language is ECMAScript.
To learn this language, previous knowledge of CSS and Html will be useful. If up to this point you did not know about CSS and Html, then you should immediately familiarize yourself.
Limitations and capabilities of JavaScriptThe following features appear when scripts are used on web pages:
- Adding various animation effects that cannot be implemented with using HTML and CSS.
- Ability to change content HTML elements and adding new tags without reloading the page.
- Response to events (response to user actions) - processing of keystrokes on the keyboard and movements of the mouse cursor.
- Perform validation of data that was entered into form fields before being sent to the server. This reduces the load on the server and speeds up the site.
- Determining the browser version and loading the required page depending on this.
This is not a complete list of scripting capabilities that have been written in this language, JavaScript functions have a much broader meaning.
In addition to the above possibilities, there are also limitations to the use of scripts:
- There is no access to files located on user computer. In general there is no access beyond the web page itself. The only exceptions can be cookies, which can be read and written from using JavaScript. Objects of this type are usually needed only to make the page load faster.
- There is no possibility of performing cross-domain requests, that is, gaining access to web pages that are located on another domain, even if they are open in adjacent tabs.
- There is no way to close tabs and windows that were opened with its help.
- There is no way to protect the original text on the page or prevent images or text from being copied from the page. However, it remains possible to add some restrictions, which JavaScript functions allow.
Such restrictions, in a sense, make it difficult for malicious code to execute.
As noted above, JavaScript is a language that adds interactivity to web pages. Using this language, those applications are created that are included in the HTML code. For example, forms or registration forms filled out by the user. JavaScript is often confused with Java, but these languages have little in common.
Some even compare JavaScript to others Ruby languages, Self , Python. But this is a separate language.
Using JavaScriptUsing JavaScript, you can make changes to the page, change element styles, and add or remove tags. It is also possible to find out about the user’s actions on the page (reducing or enlarging the working area of the screen, clicking with the mouse, pressing any keys, scrolling the page). It is possible to gain access to any element of the Html code and manipulate this element. Thus, the answer to the question “What are JavaScripts?” will be able to load data without reloading the page, enter messages, set or read cookies, and perform many other actions.
The main uniqueness of this language is that it is supported by almost all browsers and has full integration with them. All actions using JavaScript are very simple. There is no other technology that contains everything similar benefits. For example, there are not cross-browsers; they are not supported by all browsers (these are XUL, ActiveX, VBScript). There are also those that are not fully integrated with the browser. These are Silverlight, Flash, Java. On this moment There is a great development of such technology and there are JavaScript elements 2.
Alternative programming languagesIt happens that JavaScript capabilities are limited. In this case they will help following languages programming.
The most used language is Java. This language is used to describe complex algorithms, but this is not always required on a regular website. For this reason, java-applets take a long time to load and have a considerable size.
From the very beginning, Flash was designed to be cross-browser and for creating multimedia objects. For example, to create interactive areas on a website, games, banners, audio and video players. Among other things, with using Flash sockets (network connections) are created, you can work with multimedia, store objects that do not need to send requests to the server. There are convenient graphic tools development for Flash.
If we compare the disadvantages of Flash and JavaScript, the objects of which are very different, then the main disadvantage of Flash is its poor indexing by search engines. This happens because search engines go by There is also no way to select text located in a Flash container.
Silverlight, Vbscript, JavaFX, XUL
In order to complement the capabilities of JavaScript when building interfaces and communications, Silverlight, Vbscript, JavaFX, and XUL technologies are used.
They are still used less often than Flash and JavaScript. To highlight the features of each of them, we can say the following:
XUL - used to describe desktop applications and interfaces. But this is only possible if you create a program for Mozilla.
JavaFX - works on a computer only with Java, as it is an addition to this language.
Vbscript was developed by Microsoft Corporation. The basis was Visual Basic. This language is not developing in any way, is almost not used these days, and is inferior in capabilities to JavaScript.
Silverlight - was developed by Microsoft as a competitor to Flash. It also does not have much popularity, because... JavaScript strings can provide many more page scripts.
Now it’s worth discussing the everyday problems of users on the Internet. Today, it increasingly happens that a user, after visiting his page on social media. network sees in the top window the error message “JavaScript is not enabled”, “For proper operation website, please enable JavaScript", "JavaScript error". How to fix this is a serious question, because... In this case, the user has difficulty loading videos and photos.
How to enable JavaScript in Mozilla FirefoxIf the user works in Mozilla, you need to go to “Tools”, then to “Settings”. Then on the “Content” tab you need to check the box next to “Use JavaScript”.
To enable or disable JavaScript in this browser, the following steps are required: “Configuration and Google management Chrom", "Options", "Advanced", "Personal Information (Content Settings)", "JavaScript". Allow all sites using JavaScript(recommended).
How to enable JavaScript in OperaTo enable or disable JavaScript in this browser, you need to do the following:
Press the F12 key.
Selecting “Enable JavaScript”.
How to enable JavaScript in IE (Internet Explorer)To enable or disable JavaScript in Internet Explorer, you need to do the following: “Tools”, “Internet Options”, “Security” tab, “Select Internet zone”, “Other” button, “Scripts” item, “Allow scripts”.
JavaScript in VKTo solve this problem, you need to fix the JavaScript error in the VKontakte network.
What's happened JavaScript error VK?The user visited his page on the social network and tried to launch a video or audio file, but then found it in the left top corner"JavaScript error: initAddMedia is not defined" message. This message appears when there is an error
"initAddMedia".
First you need to go to “Start”, “My Computer” and Windows folder. Then go to the system32 section and the driver folder. Then to the etc folder.
Among the small number of files in this folder you need to select hosts file.
This file is then opened using Notepad. It looks like this: you need to click on right click mouse and select "Open with". Next you can select “ Text editor WordPad".
After opening this file, you need to look at the file with the entry 127.0.0.1 localhost. Any other entries are unnecessary and only complicate and block stable work audio and video files. You need to completely remove all information from the file and copy only this inscription 127.0.0.1 localhost. Next, you need to click “Save” and restart the computer. The next time you visit the VKontakte page, everything will work fine.