深入理解爬虫:网页分析

callback

callback, also known as a “call-after” function, is any executable code that is passed as an argument to other code, that other code is expected to call back (execute) the argument at a given time.

This execution may be immediate as in a synchronous callback(blocking callbacks, callbacks), or it might happen at a later time as in an asynchronous callback(deferred callbacks).

Programming languages supports callbacks in different ways, often implementing them with subroutines, lambda expressions, blocks, or function pointers. The generic, umbrella term callable unit is sometimes used.

subroutine

A subroutine is a sequence of program instructions that performs a specific task, packaged as a unit. This unit can then be used in programs wherever that particular task should be performed.

In different programming languages, a subroutine may be called a routine, subprogram, function, method, or procedure.

Event Handler

In computer programming, an event handler is a callback subroutine that handles inputs received in a program (called a listener in Java and JavaScript).

Each event is a piece of application-level information from the underlying framework, typically the GUI toolkit. GUI events include key presses, mouse movement, action selections, and timers expiring.

Event handlers are a central concept in event-driven programming.

DOM

The Document Object Model(DOM) is a cross-platform and language-independent interface that treats an XML or HTML document as a tree structure wherein each node is an object representing a part of the document.

The DOM represents a document with a logical tree.

Nodes can have event handlers attached to them.

When a web page is loaded, the browser creates a Document Object Model of the page, which is an object oriented representation of an HTML document that acts as an interface between JavaScript and the document itself. This allows the creation of dynamic web pages.