Understanding variable declaration in CoffeeScript: Navigating the absence of var”

CoffeeScript @ Freshers.in Training

CoffeeScript, a language that compiles into JavaScript, offers a unique syntax that often simplifies and enhances the readability of code. One of its notable features is the handling of variable declarations without the explicit use of the var keyword. This article delves into the mechanics of this feature, illustrating how CoffeeScript interprets variable declarations.

CoffeeScript’s variable declaration mechanism

In traditional JavaScript, the var keyword is used to declare variables. CoffeeScript, however, abstracts this requirement, making the code less verbose and arguably more elegant.

In CoffeeScript, when you assign a value to a variable that hasn’t been declared previously, the compiler automatically declares this variable at the top of the scope. This process is known as “variable hoisting,” and it ensures that all variables are declared, whether or not the var keyword is explicitly used.

Variable declaration in CoffeeScript

Let’s look at an example to understand how CoffeeScript handles variable declarations. We’ll use a simple scenario involving assigning names to variables.

CoffeeScript code

sachin = "cricketer"
manju = "artist"
ram = "engineer"
raju = "doctor"
david = "musician"
wilson = "teacher"

Equivalent JavaScript code

When compiled into JavaScript, the above CoffeeScript code would look like this:

var sachin, manju, ram, raju, david, wilson;
sachin = "cricketer";
manju = "artist";
ram = "engineer";
raju = "doctor";
david = "musician";
wilson = "teacher";


  • In the CoffeeScript code, we assigned values to six variables without using the var keyword.
  • The CoffeeScript compiler automatically declares these variables at the top of the scope in the compiled JavaScript.
  • This automatic declaration prevents variables from being global by default, a common issue in JavaScript when the var keyword is omitted.

Advantages and Caveats


  • Simpler Syntax: Reduces verbosity and enhances readability.
  • Scope Management: Helps in managing variable scopes effectively, preventing accidental global variables.


  • Potential Confusion: For those accustomed to JavaScript, this implicit declaration might be initially confusing.
  • Strict Mode Compatibility: In JavaScript’s strict mode, variables must be declared with var, let, or const. CoffeeScript handles this internally, but understanding the underlying JavaScript can be important for debugging and compatibility.
Author: user