Building JavaScript from Six Characters: A jsFuck Tutorial

JavaScript’s flexible type conversion allows strings, numbers, booleans, and objects to be created from the minimal character set []()+!, which the article calls the "golden rules": ! yields a Boolean, + yields a Number, and []+[] yields a String.

By combining these rules, simple expressions such as ![]===false, +[]===0, and []+[]==="" are shown, then extended to extract characters from built‑in strings like (![]+[])[+!![]]==="a" and to build words such as fill, filter, and find using array method names.

The article demonstrates how to retrieve additional letters via constructor functions, e.g.,

true["constructor"]+[]==="function Boolean() { [native code] }"

, and how to assemble the full alphabet by converting numbers to different bases with (12)["toString"](16)==="c".

It then shows how to obtain punctuation and HTML tags using string methods like "test"["bold"]() which returns <b>test</b>, and how to invoke the global escape function via

[]["fill"]["constructor"]("return escape(' ')")()==="%20"

.

Finally, the article explains constructing and executing arbitrary code with the Function constructor, for example Function("alert('test')")();, and concludes that using only []()+!. one can achieve Turing‑complete JavaScript, as demonstrated by the jsFuck project.