Javascript: performance of var functionName = function() {} vs function functionName() {} [duplicate]

Question

Possible Duplicate:
Does use of anonymous functions affect performance?

What are performance implications (if any) on parse and run-time when using function expression vs declaration in Javascript?

For example, what are performance characteristics and differences of the following two ways:

var functionOne = function() {
    // Some code
}

or:

function functionTwo() {
    // Some code
}

NOTE: The question is not about whether it is faster to declare function but about function execution.

Answer 1

Much more important than performance differences are the semantic differences between those two.

• A function declared with a function declaration statement (second sample) has a name that will show up in stack traces etc.
• Function declaration statements are "hoisted" to the top of their blocks and interpreted as if they actually appeared there, before any other statements in the function run.

The performance differences are probably pretty tiny, if even detectable, at least in modern runtime environments.

Answer 2

Here is a JSPerf Link, try testing on multiple browser, because results tend to vary. In chrome 10 the function statement got better score. http://jsperf.com/fn-expression-vs-statement