Article Object The Article Object is new in HTML5. The Article object represents an HTML <article> element. Note: The <article> element is not supported in Internet Explorer 8 and earlier versions. Access an Article Object You can access an <article> element by using getElementById(): Example var x = document.getElementById(“myArticle”); Try it Yourself » Create an Article Object […]
Area Object The Area object represents an HTML <area> element. Access an Area Object You can access an <area> element by using getElementById(): Example var x = document.getElementById(“myArea”); Try it Yourself » Create an Area Object You can create an <area> element by using the document.createElement() method: Example var x = document.createElement(“AREA”); Try it Yourself » Area […]
Example The type attribute specifies the media type of the target URL: <img src=”planets.gif” width=”145″ height=”126″ alt=”Planets” usemap=”#planetmap”> <map name=”planetmap”> <area shape=”rect” coords=”0,0,82,126″ alt=”Sun” href=”/images/sun.gif” type=”image/gif”> </map> Try it Yourself » Definition and Usage The type attribute specifies the Internet media type (formerly known as MIME type) of the target URL. This attribute is only used if the href attribute is set. Note: This attribute is […]
Address Object The Address object represents an HTML <address> element. Access an Address Object You can access an <address> element by using getElementById(): Example var x = document.getElementById(“myAdr”); Try it Yourself » Create an Address Object You can create an <address> element by using the document.createElement() method: Example var x = document.createElement(“ADDRESS”); Try it Yourself » Standard […]
Abbreviation Object The Abbreviation object represents an HTML <abbr> element. Access an Abbreviation Object You can access an <abbr> element by using getElementById(): Example var x = document.getElementById(“myAbbr”); Try it Yourself » Create an Abbreviation Object You can create an <abbr> element by using the document.createElement() method: Example var x = document.createElement(“ABBR”); Try it Yourself » Standard […]
In SPSS, we sometimes encounter variables that are negatively coded: lower values indicate higher agreement or more positive sentiments. Although this is not really “wrong” in any way, positive coding is more intuitive. Especially when reporting means over variables, most readers naturally expect higher means to indicate something better, not worse. So what’s the best way to reverse code variables? […]
Method Reuse With the apply() method, you can write a method that can be used on different objects. The JavaScript apply() Method The apply() method is similar to the call() method (previous chapter). In this example the fullName method of person is applied on person1: Example var person = { fullName: function() { return this.firstName + ” ” + this.lastName; } } var person1 = { firstName: “Mary”, lastName: “Doe”, } person.fullName.apply(person1); // Will return “Mary Doe” Try it […]
Method Reuse With the call() method, you can write a method that can be used on different objects. All Functions are Methods In JavaScript all functions are object methods. If a function is not a method of a JavaScript object, it is a function of the global object (see previous chapter). The example below creates an […]
The code inside a JavaScript function will execute when “something” invokes it. Invoking a JavaScript Function The code inside a function is not executed when the function is defined. The code inside a function is executed when the function is invoked. It is common to use the term “call a function” instead of “invoke a function“. It […]
JavaScript functions are defined with the function keyword. You can use a function declaration or a function expression. Function Declarations Earlier in this tutorial, you learned that functions are declared with the following syntax: function functionName(parameters) { code to be executed } Declared functions are not executed immediately. They are “saved for later use”, and will be executed later, when they are invoked (called upon). […]
Date Object The Date object is used to work with dates and times. Date objects are created with new Date(). There are four ways of instantiating a date: var d = new Date(); var d = new Date(milliseconds); var d = new Date(dateString); var d = new Date(year, month, day, hours, minutes, seconds, milliseconds); For a tutorial about date and times, read our JavaScript Date Tutorial. Date Object Properties Property Description constructor Returns the function […]
Array iteration methods operate on every array item. Array.forEach() The forEach() method Calls a function once for each array element. Example var txt = “”; var numbers = [4, 9, 16, 25]; numbers.forEach(myFunction); function myFunction(value, index, array) { txt = txt + item + “<br>”; } Try it Yourself » Note that the function takes 3 arguments: The item value The item index […]
A JavaScript function does not perform any checking on parameter values (arguments). Function Parameters and Arguments Earlier in this tutorial, you learned that functions can have parameters: functionName(parameter1, parameter2, parameter3) { code to be executed } Function parameters are the names listed in the function definition. Function arguments are the real values passed to (and received by) the function. Parameter Rules JavaScript function definitions […]
JavaScript variables can belong to the local or global scope. Global variables can be made local (private) with closures. Global Variables A function can access all variables defined inside the function, like this: Example function myFunction() { var a = 4; return a * a; } Try it Yourself » But a function can also access variables defined outside the function, like this: Example var a = 4; function myFunction() { […]
In JavaScript you cannot use these reserved words as variables, labels, or function names: abstract arguments await* boolean break byte case catch char class* const continue debugger default delete do double else enum* eval export* extends* false final finally float for function goto if implements import* in instanceof int interface let* long native new null […]
How to speed up your JavaScript code. Reduce Activity in Loops Loops are often used in programming. Each statement in a loop, including the for statement, is executed for each iteration of the loop. Statements or assignments that can be placed outside the loop will make the loop run faster. Bad: var i; for (i = 0; i […]
Avoid global variables, avoid new, avoid ==, avoid eval() Avoid Global Variables Minimize the use of global variables. This includes all data types, objects, and functions. Global variables and functions can be overwritten by other scripts. Use local variables instead, and learn how to use closures. Always Declare Local Variables All variables used in a function […]
Always use the same coding conventions for all your JavaScript projects. JavaScript Coding Conventions Coding conventions are style guidelines for programming. They typically cover: Naming and declaration rules for variables and functions. Rules for the use of white space, indentation, and comments. Programming practices and principles Coding conventions secure quality: Improves code readability Make code maintenance easier […]
Example var person = { firstName: “John”, lastName : “Doe”, id : 5566, fullName : function() { return this.firstName + ” ” + this.lastName; } }; Try it Yourself » What is “this”? In a function definition, this refers to the “owner” of the function. In the example above, this refers to the person object. The person object “owns” the fullName method. Default Binding When used alone, this refers to the Global object. In a browser the Global object is […]
“use strict”; Defines that JavaScript code should be executed in “strict mode”. The “use strict” Directive The “use strict” directive is new in JavaScript 1.8.5 (ECMAScript version 5). It is not a statement, but a literal expression, ignored by earlier versions of JavaScript. The purpose of “use strict” is to indicate that the code should be […]
