JavaScript
A prototyping-based scripting language that is used in web development to create dynamic web elements.
History of JavaScript
Development started in 1995 when the NCC hired Brendan Eich to create a
language that allowed web pages to be dynamic
(1).
After running through possible names (such as Mocha and LiveScript), it was eventually
decided that it should be named JavaScript due to its popularity at the time
(1).
This technology was integrated into NCC's propriety browser Netscape
Navigator and later adopted by many more.
Popularity
According to the tiobe index, an index where programming languages are rated based on how frequently they are used by industry professionals, JavaScript is rated #6 (2). It is a must-learn for all web developers and has been normalized in the industry for almost as long as web development has existed.
Why do we use it?
It is able to facilitate dynamic websites with relatively little code (3). Its sheer dominance in the industry also is a big influence, it's common and in many large companies tech stacks (3).