Question

On two occasions I have been asked, ‘Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?’ [...] I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question.

Charles Babbage, Passages from the Life of a Philosopher (1864)

Numbers, Booleans, and strings are the bricks that data structures are built from. But you can’t make much of a house out of a single brick. Objects allow us to group values—including other objects—together and thus build more complex structures.

The programs we have built so far have been seriously hampered by the fact that they were operating only on simple data types. This chapter will add a basic understanding of data structures to your toolkit. By the end of it, you’ll know enough to start writing some useful programs.

The chapter will work through a more or less realistic programming example, introducing concepts as they apply to the problem at hand. The example code will often build on functions and variables that were introduced earlier in the text.

The online coding sandbox for the book ( eloquentjavascript.net/code ) provides a way to run code in the context of a specific chapter. If you decide to work through the examples in another environment, be sure to first download the full code for this chapter from the sandbox page.

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.