Question

You now know that a program is built out of statements, which themselves sometimes contain more statements. Statements tend to contain expressions, which themselves can be built out of smaller expressions.

Putting statements after one another gives you a program that is executed from top to bottom. You can introduce disturbances in the flow of control by using conditional ( if , else , and switch ) and looping ( while , do , and for ) statements.

Variables can be used to file pieces of data under a name, and they are useful for tracking state in your program. The environment is the set of variables that are defined. JavaScript systems always put a number of useful standard variables into your environment.

Functions are special values that encapsulate a piece of program. You can invoke them by writing functionName(argument1, argument2) . Such a function call is an expression, and may produce a value.

This is a book about getting computers to do what you want them to do. Computers are about as common as screwdrivers today, but they contain a lot more hidden complexity and thus are harder to operate and understand. To many, they remain alien, slightly threatening things.