Function Statements and Expressions in JavaScript

JavaScript is not really taken very seriously as a programming language, when it has to be. This statement comes to my mind whenever I read the book JavaScript, Good Parts.

In JavaScript you can define a function as a statement or as an expression.ie.,

   function eat(){ document.write("Eating"); }//Statement

   var eat = function(){ document.write("Eating"); }//Expression

The main difference between the two comes in the use of the function. A function declared as a statement can be used anywhere in the script ie., even before the declaration like

      eat();//prints Eating
      function eat(){ document.write("Eating"); }//Statement

The same code will throw an error if the function were declared as an expression.

      eat();//Uncaught TypeError: Property 'eat' of object [object DOMWindow] is not a function
      var eat = function(){ document.write("Eating"); }//Statement

So we’ll have to either stick to using functions as statements or expressions in the code. Need to be careful when we use both.