Function Declarations versus Function Expressions

Function declarations are available in an execution context before any code is executed.

 
<!DOCTYPE html>
<html>
<head>
    <title>Example</title>
    <script type="text/javascript">
        document.writeln(sum(10,10)); 
        
        function sum(num1, num2){
         return num1 + num2; 
        
        } 
       
    </script>
</head>
<body>
</body>
</html>
Click to view the demo

The function declaration is equivalent with variable declaration:

 
<!DOCTYPE html>
<html>
<head>
    <title>Example</title>
    <script type="text/javascript">
    
        document.writeln(sum(10,10));  // ERROR
        var sum = function(num1, num2){ 
            return num1 + num2; 
        }; 

       
    </script>
</head>
<body>
</body>
</html>
Click to view the demo
Home 
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    Essential Types  

Function:
  1. The Function Type
  2. Function Declarations versus Function Expressions
  3. Functions as Values
  4. Returning a function from a function
  5. Function arguments
  6. this for function context
  7. Function caller
  8. Function length property
  9. Function apply()
  10. Function.call() method
  11. Function's bind() method
  12. Function toLocaleString() and toString()