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JavaScript – Syntax ”; Previous Next JavaScript Syntax JavaScript syntax comprises a set of rules that define how to construct a JavaScript code. JavaScript can be implemented using JavaScript statements that are placed within the <script>… </script> HTML tags in a web page. You can place the <script> tags, containing your JavaScript, anywhere within your web page, but it is normally recommended that you should keep it within the <head> tags. The <script> tag alerts the browser program to start interpreting all the text between these tags as a script. A simple syntax of your JavaScript will appear as follows. <script …> JavaScript code </script> The script tag takes two important attributes − Language −This attribute specifies what scripting language you are using. Typically, its value will be javascript. Although recent versions of HTML (and XHTML, its successor) have phased out the use of this attribute. Type −This attribute is what is now recommended to indicate the scripting language in use and its value should be set to “text/javascript”. JavaScript has become default lannguage in HTML5, and modern browsers, so now adding type is not required. So your JavaScript segment will look like − <script language = “javascript” type = “text/javascript”> JavaScript code </script> Your First JavaScript Code Let us take a sample example to print out “Hello World”. We call document.write method which writes a string into our HTML document. This method can be used to write text, HTML, or both. Take a look at the following code − <html> <head> <title> Your first JavaScript program </title> <head> <body> <script language = “javascript” type = “text/javascript”> document.write(“Hello World!”) </script> </body> </html> This code will produce the following result − Hello World! JavaScript Values In JavaScript, you can have two types of values. Fixed values (Literals) Variables (Dynamic values) JavaScript Literals In the below code, 10 is a Number literal and ‘Hello’ is a string literal. <html> <body> <script> document.write(10); // Number Literal document.write(“<br />”); // To add line-break document.write(“Hello”); // String Literal </script> </body> </html> This code will produce the following result − 10 Hello JavaScript Variables In JavaScript, variables are used to store the dynamic data. You can use the below keyword to define variables in JavaScript. var let const You can use the assignment operator (equal sign) to assign values to the variable. In the below code, variable a contains the numeric value, and variable b contains the text (string). <html> <body> <script> let a = 5; // Variable Declaration document.write(a); // Using variable document.write(“<br>”); let b = “One”; document.write(b); </script> </body> </html> This code will produce the following result − 5 One Whitespace and Line Breaks JavaScript ignores spaces, tabs, and newlines that appear in JavaScript programs. 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 JavaScript are generally followed by a semicolon character, just as they are in C, C++, and Java. JavaScript, 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. <script> var1 = 10 var2 = 20 </script> But when formatted in a single line as follows, you must use semicolons − <script> var1 = 10; var2 = 20; </script> It is a good programming practice to use semicolons. Case Sensitivity JavaScript is a case-sensitive language. 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 JavaScript. In the code below, we compare the ‘time’ and ‘Time’ strings, which returns false. <html> <body> <script> let a = “time”; let b = “Time”; document.write(“a == b? ” + (a == b)); </script> </body> </html> This code will produce the following result − a == b? false Care should be taken while writing variable and function names in JavaScript. JavaScript and Camel Case Pascal Case − We can create variables like SmartWatch, MobileDevice, WebDrive, etc. It represents the upper camel case string. Lower Camel Case − JavaScript allows developers to use variable names and expression names like smartwatch, mobileDevice, webDriver, etc. Here the first character is in lowercase. Underscore − We can use underscore while declaring variables like smart_watch, mobile_device, web_driver, etc. JavaScript doesn’t allow adding the hyphen in variable name or expression name. JavaScript Keywords JavaScript contains multiple keywords which we can use for a particular task. For example, the function keyword can be used to define the function. The let, var, and const keywords can be used to define variables. Let’s understand the use of the keyword via the example below. Example In this example, we used the function keyword to define the function. We used the var keyword inside the function to define the sum variable. Also, we used the let and const keywords outside the function to define two variables and initialize them with values. After that, we called the function using the function name and passed variables as an argument. <html> <body> <script> function getSum(first, second) { var sum = first * second; document.write(“The product of ” + first + ” and ” + second + ” is ” + sum); } let first = 3; const second = 4; getSum(first, second); </script> </body> </html> This code will produce the following result − The product of 3 and 4 is 12 JavaScript doesn’t allow to use the of keywords as a variable or expression name. JavaScript Identifiers In JavaScript, identifiers are the name of variables, functions, objects, etc. For example, p is an identifier in the below code. <script> pet p = 90; </script> The ”test” is an identifier in the below code. <script> function test() { } </script> Here are the rules which you should follow to define valid