2.1 Variables & Assignment

>>>

var a, b

Variable names are defined using the var keyword. Several variables can be named in a single statement.

>>>

var a = 2

Optionally, an initial value can be provided. It is not an error to reuse an existing variable name. It will create a new variable that shadows (hides) the previous one.

>>>

undefined

If no value was specified when declaring the variable, undefined is used as the default.

>>>

b = 3

The = assignment operator is used to change the value of a variable.

>>>

c = 5

Beware! If a variable name hadn't been previously defined with var, a new global variable is created by the assignment. It is a common cause for bugs.

>>>

c += 1

The +=, -=, *=, /= and %= modifying assignment operators allows for easy updates. A few others also exist, which we'll see later.

>>>

++c

The ++ and -- operators increment or decrement a numeric variable and return its value. If placed after the variable, the previous value is returned (instead of the updated one).

>>>

The console allows you to interact with the course material and examples. Use the following keys:

<Enter> — Execute the code
<Shift + Enter> — Add line break
<Arrow-Up> — Previous command in history
<Arrow-Down> — Next command in history

A special logging function is also available:

print(value) — Prints a value to the console.
print(value, true) — Prints a debug version of a value.

Console Learner — An interactive JavaScript course.