Lesson 1.7: From pseudocode to JavaScript

JavaScript is a real language and it's already in your browser. The ideas are the pseudocode ones; the words change.

The idea

Pseudocode is for thinking, but it doesn't run. JavaScript does: it's a real programming language and every browser ships with it. Nothing to install.

Open the console

The console is a corner of the browser where you type JavaScript and it runs straight away.

Open a new tab.
Press F12 (on a Mac, Cmd + Option + J) and pick the Console tab.
Type this and press Enter:

JavaScript

console.log("Hello, world");

Console

Hello, world

To write several lines without running them, press Shift + Enter at the end of each one.
If undefined shows up after a line, it isn't an error: the console shows what each instruction returns, and console.log() returns nothing.
If you paste code, the console may ask you to type "allow pasting" first. It's a protection against scams: only paste code you understand.

Same ideas, other words

Pseudocode	JavaScript
`Write "Hello"`	`console.log("Hello");`
`Read name`	`let name = prompt("Name?");`
`age ← 30`	`let age = 30;`
`If … Then … EndIf`	`if (…) { … }`
`While … Do … EndWhile`	`while (…) { … }`
`Function … EndFunction`	`function name() { … }`

The next lessons go through them one by one.

The same program, twice

Pseudocode

Algorithm Greet
    Write "What's your name?"
    Read name
    Write "Hello, ", name
EndAlgorithm

JavaScript

let name = prompt("What's your name?");
console.log("Hello, " + name);

prompt() opens a window with the question and returns what you type.
+ joins pieces of text.
; marks the end of each instruction.
There's no Algorithm or EndAlgorithm: the program is what you write.

Try it

Exercise

In the console, write a program that asks for a name and a city and answers, for example, "Ana lives in Seville". It's the exercise from 1.2, for real this time.

Show the solution

JavaScript

let name = prompt("What's your name?");
let city = prompt("Which city do you live in?");
console.log(name + " lives in " + city);

Notice the spaces inside " lives in ": without them you'd get "Analives inSeville".

Summary

JavaScript is a real language and it runs in the browser.
The console (F12) runs it straight away.
console.log() writes; prompt() asks.