Variables in JavaScript

What you'll learn

  • Create variables with var and store strings and numbers.
  • Pick clear names that make code readable.
  • Print values to inspect them in the Code Editor console.
  • Understand how to wrap values as Earth Engine objects when needed.

Why this matters

Variables are the foundation for every script. In Earth Engine, you store images, geometries, dates, and results in variables so you can reuse them without retyping long expressions.

What Is a Variable?

A variable is a labeled container for data.

var city = 'Gainesville';
  • var: declare a new variable.
  • city: the label you will reference later.
  • =: assignment operator.
  • 'Gainesville': the value stored (a string).

Storing and printing values

var population = 140398;
var latitude = 29.6516;
var longitude = -82.3248;

print('Population:', population);
print('Lat/Lon:', latitude, longitude);

Expected output

Console lines showing the population and coordinates you stored.

Text vs numbers

Strings need quotes ('Miami'), numbers do not (25.76).

Naming variables

// Hard to read
var x = 29.6516;
var y = -82.3248;

// Clear and descriptive
var latitude = 29.6516;
var longitude = -82.3248;
var zoomLevel = 9;

Use camelCase for multiple words (studyArea). Avoid reserved words (like var, function).

Pro tips

  • Declare once, reuse often: set var roi and pass it to filters and reducers.
  • Use print() whenever you are unsure what a variable contains.
  • Keep variable scope tight-declare inside functions when only used there.

Important: client vs server

Plain JavaScript variables live in your browser. Earth Engine computations need ee objects (for example, ee.Number(5) instead of 5 when used in server math). See Client vs Server for details.

Try it yourself

  1. Create myCity as a string and myLatitude/myLongitude as numbers.
  2. Print them together in one print call.
  3. Wrap the numbers as ee.Number and add 1 using .add().

Common mistakes to avoid

  • Missing quotes for text: var city = Gainesville; will error.
  • Spaces in names: var study area is invalid.
  • Starting with a number: var 2ndCity is invalid.
  • Mismatched quotes: 'Gainesville" will error.

Additional resources

W3Schools: JavaScript Variables