Blocking operation

A blocking operation requires the program to halt while it is waiting for a slow resource.

Typically, this is either a hardware resource (such as a disk drive), or a network resource (such as an HTTP request). Because the request cannot require a result from a slow resource, it blocks subsequent operation until it is complete, even if the computer or program still has available resources such as CPU or memory available.


A callback is a function that is “called back” to after a blocking operation. Typically, this is an I/O operation such as disk access. Callbacks can take parameters.


See Pseudoclass.


A unit of code that can be invoked with a set of variable parameters. It may pass a single return. In JavaScript, functions also have a context, which defines the value of the reserved this variable. Functions in JavaScript are considered first class in that they can also be treated as variables or properties of objects.


A function that is a property of an object.

See Also Function.

Nonblocking operation

A nonblocking operation is one that does not block.

See Also Blocking operation.


A pseudoclass is a way of creating an abtract object in JavaScript that is intended to be initialized into an object. Pseudoclasses should be turned into objects using the new keyword. Pseudoclass names start with a leading capital by convention to differentiate them from other kinds of objects. For example, Server would be a pseudoclass, and server might be an instance of that pseudoclass.