JavaScript 第13页

In JavaScript, a piece of information is a value. There are different kinds of values. The kind you're most familiar with are numbers. A string value is characters - such as a word or words - enclosed in quotes.

Events are actions that the user preforms while visiting your page. Submitting a form and moving a mouse over an image are two examples of events. JavaScript deals with events using commands called event handlers. An action by the user on the page triggers an event handler in your script. Some common JavaScript event handlers are listed in this post.

While reading JavaScript codes, you may find "?" operator in a high frequency.

(condition) ? truePart : falsePart; is rough equivalent of:

if (condition) {
    truePart;
}
else {
    falsePart;
}

All these properties are accessed from the window object via the period operator (for example, window.name).

Ajax (also AJAX; short for asynchronous Javascript and XML) is a group of interrelated Web develoment techniques used on the client-side to create asynchronous Web appications. With Ajax, web aplications can send data to and retrieve from a server asynchronously (in the background) without interfering with the display and behavior of the existing page. Data can be retrieved using the XMLHttpRequest object. Despite the name, the use of XML is not required (JSON is often used in teh AJAJ variant), and the requests do not need to be asynchronous.

Ajax is not a single technology, but a group of technologies. HTML and CSS can be used in combination to mark up and style information. The DOM is accessed with JavaScript to dynamically display - and allow the user to interact with - the information presented. JavaScript and the XMLHttpRequest object provide a method for exchanging data asynchronously between browser and server to avoid full page reloads.

Summary of Metacharacters in Regular Expression