Joey Javas

JavaScript is an untyped language. This means that a variable can hold any datatype. It also means that a variable may be assigned data of one particular datatype and then later be given data of a different datatype. For example:

var x = 'Joey JavaScript';
x = true;
x = 1;

In the preceding example, the variable x is initialized containing the string datatype. It is than assigned a value that results in it holding the Boolean datatype. Finally, it is assigned 1, giving it the number datatype.

Many other languages are strongly typed, which means that a variable can only be associated with the datatype to which it is declared. This makes it easier to enforce datatyping rules within programs. JavaScript is untyped, however, which makes it more difficult to enforce datatyping rules but results in simplicity in developing programs quickly.

Once an XMLHttpRequest has been initiated, sent and a response received, the XMLHttpRequest will have a responseText property. This property contains the server response, excluding headers.

Note that responseText is not fully loaded until the XMLHttpRequest readyState is 4. The responseText property can also contain a partial portion of the final result text if readyState is 3, which means that data is in the process of being received from the server.

To access this property: If an XMLHttpRequest call is saved in a variable named objXHR, the responseText can be accessed as objXHR.responseText.

Related articles:
JavaScript XMLHttpRequest readyState values

Submitting a form can be accomplished with JavaScript by accessing the named form and then calling the submit method on it.

<form name="frmTest" action="somepage.html”" method="post">
First Name: <input type="text" name="FirstName">
<input type="button" onclick="document.frmTest.submit();" value="Submit Form">
</form>

The JavaScript occurs with the onclick attribute of the button input type. It uses the document object model to access the named form and calls the submit method on it.

There are a few different ways in which a new page can be loaded in a browser through JavaScript.

window.document.location.href = 'http://www.joeyjavascript.com';
window.document.location = 'http://www.joeyjavascript.com';
window.location = 'http://www.joeyjavascript.com';
location = 'http://www.joeyjavascript.com';
document.location.href = 'http://www.joeyjavascript.com';
document.location = 'http://www.joeyjavascript.com';

As seen in the previous examples, both the window object and the document object have a location property that can be assigned a URL. It is generally preferable to set the location property of the window object, as the document object was originally intended as a read-only property and some older browsers still treat it as such.

Relative or absolute URLs can be assigned as the page to be loaded.

There is also a replace method that can be called on the location property, as follows:

window.location.replace('http://www.joeyjavascript.com');

Using this method will cause the requested page to replace the current page in the browser and is not a new page request. Hence, the page it replaces is no longer in the browser history.

A common mistake when using the getElementById function in Firefox is failing to set the id attribute of the element being accessed. This will work in Internet Explorer because it treats the name attribute as the id attribute in the case where the id attribute is not provided. Firefox, however, is not forgiving on this point. The id attribute of an element must be provided in order to access that element via the getElementById function.

Example:

<input type=”text” name=”FirstName” id=”FirstName”>

Related articles:
Accessing Form Elements with JavaScript

Without the id=”FirstName”, this element cannot be accessed by the getElementById function in Firefox.

JavaScript provides the conditional operator as a shortcut for an “if” statement. The conditional operator consists of a question mark (?) and a colon (:), as shown below:

var intTest = 1;
intTest == 1 ? x = 1 : x = 2;
document.write(x);

The expression preceding the question mark must evaluate to a Boolean value. If the result of this expression is true, the expression following the question mark but preceding the colon runs; otherwise, the expression after the colon runs.