This page teaches you how to find and access HTML elements in an HTML page. Finding HTML Elements Often, with JavaScript, you want to manipulate HTML elements. To do so, you have to find the elements first. There are a couple of ways to do this: Finding HTML elements by id Finding HTML elements by […]
The HTML DOM document object is the owner of all other objects in your web page. The HTML DOM Document Object The document object represents your web page. If you want to access any element in an HTML page, you always start with accessing the document object. Below are some examples of how you can […]
HTML DOM methods are actions you can perform (on HTML Elements). HTML DOM properties are values (of HTML Elements) that you can set or change. The DOM Programming Interface The HTML DOM can be accessed with JavaScript (and with other programming languages). In the DOM, all HTML elements are defined as objects. The programming interface is the properties and methods of […]
With the HTML DOM, JavaScript can access and change all the elements of an HTML document. The HTML DOM (Document Object Model) When a web page is loaded, the browser creates a Document Object Model of the page. The HTML DOM model is constructed as a tree of Objects: The HTML DOM Tree of Objects With the object model, JavaScript gets […]
JavaScript Form Validation HTML form validation can be done by JavaScript. If a form field (fname) is empty, this function alerts a message, and returns false, to prevent the form from being submitted: JavaScript Example function validateForm() { var x = document.forms[“myForm”][“fname”].value; if (x == “”) { alert(“Name must be filled out”); return false; } } The function can be […]
Progress Object The Progress Object is new in HTML5. The Progress object represents an HTML <progress> element. The <progress> element represents the progress of a task. Access a Progress Object You can access a <progress> element by using getElementById(): Example var x = document.getElementById(“myProgress”); Try it Yourself » Create a Progress Object You can create a […]
Strong Object The Strong object represents an HTML <strong> element. Access a Strong Object You can access a <strong> element by using getElementById(): Example var x = document.getElementById(“myStrong”); Try it Yourself » Create a Strong Object You can create a <strong> element by using the document.createElement() method: Example var x = document.createElement(“STRONG”); Try it Yourself » Standard […]
Textarea Object The Textarea object represents an HTML <textarea> element. Access a Textarea Object You can access a <textarea> element by using getElementById(): Example var x = document.getElementById(“myTextarea”); Try it Yourself » Tip: You can also access a <textarea> element by searching through the elements collection of a form. Create a Textarea Object You can create a <textarea> element […]
Caption Object The Caption object represents an HTML <caption> element. Access a Caption Object You can access a <caption> element by using getElementById(): Example var x = document.getElementById(“myCaption”); Try it Yourself » Create a Caption Object You can create a <caption> element by using the document.createElement() method: Example var x = document.createElement(“CAPTION”); Try it Yourself » Tip: You […]
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 […]
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 […]
