It is always difficult to pen the first few words, especially on a subject like JavaScript. This difficulty arises primarily because so many things have been said about this language. JavaScript has been the Language of the Web—lingua franca, if you will, since the earliest days of the Netscape Navigator. JavaScript went from a tool of the amateur to the weapon of the connoisseur in a shockingly short period of time.
JavaScript is the most popular language on the web and open source ecosystem. http://githut.info/ charts the number of active repositories and overall popularity of the language on GitHub for the last few years. JavaScript's popularity and importance can be attributed to its association with the browser. Google's V8 and Mozilla's SpiderMonkey are extremely optimized JavaScript engines that power Google Chrome and Mozilla Firefox browsers, respectively.
Although web browsers are the most widely used platforms for JavaScript, modern databases such as MongoDB and CouchDB use JavaScript as their scripting and query language. JavaScript has become an important platform outside browsers as well. Projects such as Node.js and io.js provide powerful platforms to develop scalable server environments using JavaScript. Several interesting projects are pushing the language capabilities to its limits, for example, Emscripten (http://kripken.github.io/emscripten-site/) is a Low-Level Virtual Machine (LLVM)-based project that compiles C and C++ into highly optimizable JavaScript in an asm.js format. This allows you to run C and C++ on the web at near native speed.
JavaScript is built around solid foundations regarding, for example, functions, dynamic objects, loose typing, prototypal inheritance, and a powerful object literal notation.
While JavaScript is built on sound design principles, unfortunately, the language had to evolve along with the browser. Web browsers are notorious in the way they support various features and standards. JavaScript tried to accommodate all the whims of the browsers and ended up making some very bad design decisions. These bad parts (the term made famous by Douglas Crockford) overshadowed the good parts of the language for most people. Programmers wrote bad code, other programmers had nightmares trying to debug that bad code, and the language eventually got a bad reputation. Unfortunately, JavaScript is one of the most misunderstood programming languages (http://javascript.crockford.com/javascript.html).
Another criticism leveled at JavaScript is that it lets you get things done without you being an expert in the language. I have seen programmers write exceptionally bad JavaScript code just because they wanted to get the things done quickly and JavaScript allowed them to do just this. I have spent hours debugging very bad quality JavaScript written by someone who clearly was not a programmer. However, the language is a tool and cannot be blamed for sloppy programming. Like all crafts, programming demands extreme dedication and discipline.
In 1993, the Mosaic browser of National Center for Supercomputing Applications (NCSA) was one of the first popular web browsers. A year later, Netscape Communications created the proprietary web browser, Netscape Navigator. Several original Mosaic authors worked on Navigator.
In 1995, Netscape Communications hired Brendan Eich with the promise of letting him implement Scheme (a Lisp dialect) in the browser. Before this happened, Netscape got in touch with Sun Microsystems (now Oracle) to include Java in the Navigator browser.
Due to the popularity and easy programming of Java, Netscape decided that a scripting language had to have a syntax similar to that of Java. This ruled out adopting existing languages such as Python, Tool Command Language (TCL), or Scheme. Eich wrote the initial prototype in just 10 days (http://www.computer.org/csdl/mags/co/2012/02/mco2012020007.pdf), in May 1995. JavaScript's first code name was Mocha, coined by Marc Andreessen. Netscape later changed it to LiveScript, for trademark reasons. In early December 1995, Sun licensed the trademark Java to Netscape. The language was renamed to its final name, JavaScript.