Course · Free

JavaScript Fundamentals

Know another language? Learn the core of JavaScript by building a mock interview booking page: variables, types, conditionals, loops, functions, arrays and objects. Predict what each line prints.

Lessons

102

Steps

About 1.5 hours

Duration

Your own

Pace

Short on time? Read the recap and interview answers

Curriculum

01
let, const and var
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Three ways to name a value, and the bug each one prevents.
02
The eight types
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A duration, a topic, a yes or no, and nobody yet: each is a different kind of value.
03
Type conversion
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The duration arrives from the URL as a string. Adding a 15-minute buffer gives 9015.
04
Comparing values: == and ===
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The menu gives the string 10, but the open hours are numbers. Is the slot free?
05
Conditionals and loops
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The page must label long sessions, sort slots into morning and afternoon, and make a button for every open hour.
06
||, &&, ?? and ?.
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No duration in the URL, a reminder at 0 that becomes 15, and a crash on the interviewer's name.
07
Functions: declarations, expressions and arrows
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Every slot needs the same label logic, and slot buttons made in a loop book the wrong hour.
08
Arrays: the basics
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The page keeps a list of open hours. Slots open, pass and get booked, so the list keeps changing.
09
Objects: the basics
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A booking has a topic, a duration and an hour that belong together.
Final
The fundamentals challenge
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Twelve questions from across the course. Pass it to claim your certificate.