Section quiz

What JavaScript is, and how to run it

Nine questions on the three layers, semicolons you did not write, the eight types, the two kinds of nothing, and how a name comes to exist.

Questions are shuffled within each part, and so are the answers. You can retake it as often as you like.

0 of 9 answered

Part 1: The machine and the shape of a program

Question 1

A file begins with import { readFile } from "node:fs/promises";. Which dialect is the rest of the file in?

A.Strict inside functions and sloppy at the top levelB.Strict, because a file containing import is a module and every module is strictC.Sloppy, unless it also starts with "use strict";D.It depends on whether the file is named .js or .mjs

Question 2

Inside a function, the word return is alone on one line and total * 2; is on the line below it. What does the function give back?

A.total * 2, because JavaScript reads ahead to the semicolonB.undefined, but only in strict modeC.undefined, and the line below is evaluated and thrown awayD.A SyntaxError, because return has no value after it

Question 3

A file has const sum = a + b on one line and (a + b).toString() on the next, with no semicolons anywhere. What happens?

A.A TypeError about b not being a function, because the parser reads a + b(a + b)B.It runs. The line break ends the first statementC.It runs, but sum ends up holding text instead of a numberD.A SyntaxError, because the second line has no semicolon in front of it

Question 4

Which of these names is defined by the ECMAScript specification itself, rather than supplied by whatever host is running your code?

A.documentB.consoleC.MathD.setTimeout

Question 5

Which of these is not an expression?

A."a" + "b"B.const price = 1C.Math.max(1, 2)D.price

Part 2: Values, names and absence

Question 6

function pour(ml = 250) { return ml; } is called as pour(null). What comes back?

A.A TypeError, because null is not a numberB.0, because null becomes 0 when a number is wantedC.null, because a default parameter fires only for undefinedD.250, because null means no value was supplied

Question 7

const user = { name: "ada" }; then user.name = "grace";. What happens on the second line?

A.Nothing visible. The write to a const is ignored in silenceB.It works, and user.name is now "grace"C.TypeError: Assignment to constant variable.D.SyntaxError, caught before the program starts

Question 8

typeof null gives "object". What should you conclude from that?

A.null is an object with no properties on itB.typeof converts null to an object before reporting on itC.null is a reference pointing at nothing, and references are objectsD.Nothing about null. It is a bug from the first implementation, kept because too much code depends on it, and null is a primitive

Question 9

console.log(total); let total = 5; What do you see?

A.5, because the engine reads the whole file before running itB.ReferenceError: total is not definedC.ReferenceError: Cannot access 'total' before initializationD.undefined, because the declaration is hoisted to the top

9 questions left to answer.