whether what you are doing is working or not, and, hopefully, to be

tempted to ((experiment)) and go beyond the exercises.

When reading this book in your browser, you can edit (and run) all

example programs by clicking on them.

ifdef::book_target[]

press Command-Option-I. If that does not work, search through the

menus for an item named “web console” or “developer tools”.

When running the examples, or your own code, on the pages of this

book, `console.log` output will be shown after the example, instead of

in the browser's JavaScript console.

[source,javascript]

----

in an _((infinite loop))_. A program stuck in an infinite loop will

never finish running, which is usually a bad thing.

If you create an infinite loop in one of the examples on these pages,

you'll usually be asked whether you want to stop the script after a

few seconds. If that fails, you will have to close the tab that you're

working in, or on some browsers close your whole browser, in order to

recover.

(((continue keyword)))The `continue` keyword is similar to `break`, in

that it influences the progress of a loop. When `continue` is

Each exercise starts with a problem description. Read that and try to

solve the exercise. If you run into problems, consider reading the

Full solutions to the exercises are not included in this

book, but you can find them online at

http://eloquentjavascript.net/code[_eloquentjavascript.net/code_].

// → 3

----

Most exercises contain a piece of code that you can modify to solve

the exercise. Remember that you can click code blocks to edit them.

----

// Your code here.

----

!!hint!!

weed out a significant percentage of programmer candidates. So if you

solved it, you're now allowed to feel good about yourself.)

[source,javascript]

----

// Your code here.

----

!!hint!!

((variable)) `size = 8` and change the program so that it works for

any `size`, outputting a grid of the given width and height.

[source,javascript]

----

// Your code here.

----

!!hint!!

argument. We can do that ourselves now. Write a function `min` that

takes two arguments and returns their minimum.

// test: no

console.log(min(0, -10));

// → -10

----

!!hint!!

(((stack overflow)))Test it on 50 and 75. See how it behaves on -1.

Why? Can you think of a way to fix this?

// test: no

console.log(isEven(-1));

// → ??

----

!!hint!!

to be counted (rather than counting only uppercase "B" characters).

Rewrite `countBs` to make use of this new function.

// test: no

console.log(countChar("kakkerlak", "k"));

// → 4

----

!!hint!!

ifdef::html_target[]

++++

<table style="border-collapse: collapse; margin-left: 1em;"><tr>

<td style="vertical-align: middle"><em>ϕ</em> =</td>

<td style="padding-left: .5em">

</span></div>

</td>

</tr></table>

++++

endif::html_target[]

pass:[\begin{equation}\phi = \frac{n_{11}n_{00}-n_{10}n_{01}}{\sqrt{n_{1\bullet}n_{0\bullet}n_{\bullet1}n_{\bullet0}}}\end{equation}]

number of measurements where the first measurement (pizza) is false

(0) and the second measurement (squirrelness) is true (1). In this

sum of all measurements where the first variable is true, which is 10

refers to the sum of the measurements where the squirrel variable is false.

(((correlation)))(((phi coefficient)))So for the pizza table, the part

above the division line (the dividend) would be 1×76 - 9×4 = 40, and

the part below it (the divisor) would be the square root of

comes out to _ϕ_ ≈ 0.069, which is tiny. Eating ((pizza)) does not

appear to have influence on the transformations.

translation of the _ϕ_ formula into JavaScript. `Math.sqrt` is the

square root function, as provided by the `Math` object in a standard

JavaScript environment. We have to sum two fields from the table to

the sums of rows or columns are not stored directly in our data

structure.

7, 9]`. Make sure it also works with negative step values so that

`range(5, 2, -1)` produces `[5, 4, 3, 2]`.

// test: no

console.log(range(5, 2, -1));

// → [5, 4, 3, 2]

----

!!hint!!

link:03_functions.html#pure[previous chapter], which variant do you

expect to be useful in more situations? Which one is more efficient?

// test: no

console.log(arrayValue);

// → [5, 4, 3, 2, 1]

----

!!hint!!

(((recursion)))If you haven't already, also write a recursive version

of `nth`.

// test: no

console.log(nth(arrayToList([10, 20, 30]), 1));

// → 20

----

!!hint!!

comparison. But you have to take one silly exception into account: by

a historical accident, `typeof null` also produces `"object"`.

// test: no

console.log(deepEqual(obj, {here: {is: "an"}, object: 2}));

// → true

----

!!hint!!

= Higher-Order Functions =

[chapterquote="true"]

[quote, Master Yuan-Ma, The Book of Programming]

Tzu-li and Tzu-ssu were enlightened.

____

[chapterquote="true"]

[quote, C.A.R. Hoare, 1980 ACM Turing Award Lecture]

____

(((vocabulary)))The second is shorter and easier to interpret. But

_simmer_, _chop_, and, I guess, _vegetable_.

When programming, we can't rely on all the words we need to be waiting

the `concat` method to “flatten” an array of arrays into a single

array that has all the elements of the input arrays.

// test: no

// Your code here.

// → [1, 2, 3, 4, 5, 6]

----

=== Mother-child age difference ===

it easy to find a person's object from their name, might be useful

here.

// test: no

// include_code

// → 31.2

----

!!hint!!

((century)) by taking their year of death, dividing it by 100,

and rounding it up, as in `Math.ceil(person.died / 100)`.

// test: no

// 20: 84.7

// 21: 94

----

!!hint!!

methods, except that they take the array as their first argument

rather than being a method.

// test: no

console.log(some([2, 3, 4], isNaN));

// → false

----

!!hint!!