Console Learner — An interactive JavaScript course.

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.
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.
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).

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