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Asynchronous Definition

This is a common world you are listen in computer and web applications programming . Asynchronous is the opposite of word synchronous , which means existing or occurring at the same time . The its obvious asynchronous meaning not occurring same time .  Word “async” is abbriviation of Asynchronous .

This term is used to control timings to loading something in program. When you set a script loading as Asynchronous , in program, then it means your program will not wait for loading the script and other codes are executed .  

Asynchronous Advertisement script Still loading after page load
Asynchronous Advertisement script Still loading after page load

Example

Suppose you are browsing www.slashgear.com a blog on internet . In the blog there are some of advertisements in top bar ,sidebar or any other location on webpage .

Refresh the page you will notice that sidebar advertisements loading process in complete after complete page load . This is example of Asynchronous loading of javascript script

Advertisement script after loading
Advertisement script after loading

Where Asynchronous are usable

Asynchronous or Asynchrony or async is useful to speed up loading of programs ,because program don’t wait for finish the script loading .

In websites ,blogs and web application it reduce the loading time of website . So it reduce the drop off rate of website .

When you execute web scripts asynchronously ,your webpage start loading on even slow internet connections this is a major benefit.

Disadvantage

These type of timing controls are less secure . This is the reason ,banking website and online payment site etc are not preferred Asynchronously loading there programs ,scripts or function .