ABSTRACT
This chapter introduces the core features of JavaScript, including how to run programs, the language’s basic data types, arrays and objects, loops, conditionals, functions, and modules. All of these concepts should be familiar if one have programmed before. JavaScript has the usual datatypes, though unlike C, Python, and many other languages, there is no separate type for integers: it stores all numbers as 64-bit floatingpoint values, which is accurate up to about 15 decimal digits. A JavaScript program can also make choices: it executes the body of an if statement if and only if the condition is true. The argument made by JavaScript’s advocates is that an empty array is there, it just happens to be empty, but this behavior is still a common cause of bugs. When testing an array, check that Array.length is zero.
