What is the difference between these two?

Question

I saw the following JavaScript functions works exactly same, Then what is the difference between them other than syntax. The function are:

var functionName=function(){
    //some code here
}; 

function functionName(){
    //some code here
} 

I call them in the same way as:

functionName();

Please dont' tell me there syntax is different, Other than that is there any difference like

1)speed of execution
2)Memory utilization etc.

Thanks in advance!

Answer 1

This has been answered many times in StackOverflow. It is just the way of naming. So taking up some points from the answers, I would say:

1. Function declarations and variable declarations are always moved ("hoisted") invisibly to the top of their containing scope by the JavaScript interpreter. Function parameters and language-defined names are, obviously, already there.

2. Advantages & Disadvantages:

   There are few advantages to naming functions:

   • names for meta analysis. functionInstance.name will show you the name.
   • Far more importantly, the name will be printed in stack traces.
   • names also help write self documenting or literate code.

   There is a single disadvantage to named functions expressions

   • IE has memory leaks for NFE

3. Another main difference

   The difference is that functionTwo is defined at parse-time for a script block, whereas functionOne is defined at run-time. For example:

   <script>
     // Error
     functionOne();
   
     var functionOne = function() {
     }
   </script>
   
   <script>
     // No error
     functionTwo();
   
     function functionTwo() {
     }
   </script>
   

References

1. var functionName = function() {} vs function functionName() {}
2. Are named functions or anonymous functions preferred in JavaScript?
3. Named function expressions demystified
4. Function Declarations vs. Function Expressions.
5. var functionName = function() {} vs function functionName() {}

Answer 2

1. 1st one is Named Function Expressions, which should return some value to the caller.
2. 2nd one is just a function, it's upto you whether you return value or not