Javascript switch vs. if...else if...else

Question

Guys I have a couple of questions:

1. Is there a performance difference in Javascript between a switch statement and an if...else if....else?
2. If so why?
3. Is the behavior of switch and if...else if...else different across browsers? (FireFox, IE, Chrome, Opera, Safari)

The reason for asking this question is it seems that I get better performance on a switch statement with approx 1000s cases in Firefox.

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Edited Unfortuantly this is not my code the Javascript is being produced serverside from a compiled library and I have no access to the code. The method that is producing the javascript is called

CreateConditionals(string name, string arrayofvalues, string arrayofActions)

note arrayofvalues is a comma separated list.

what it produces is

function [name] (value) {
  if (value == [value from array index x]) {
     [action from array index x]
  }
}

Note: where [name] = the name passed into the serverside function

Now I changed the output of the function to be inserted into a TextArea wrote some javascript code to parse through the function and convert it to a set of case statments. finally I run the function and it runs fine but performance differs in IE and Firefox.

Answer 1

Is there a preformance difference in Javascript between a switch statement and an if...else if....else?

I don't think so, switch is useful/short if you want prevent multiple if-else conditions.

Is the behavior of switch and if...else if...else different across browsers? (FireFox, IE, Chrome, Opera, Safari)

Behavior is same across all browsers :)

Answer 2

1. If there is a difference, it'll never be large enough to be noticed.
2. N/A
3. No, they all function identically.

Basically, use whatever makes the code most readable. There are definitely places where one or the other constructs makes for cleaner, more readable and more maintainable. This is far more important that perhaps saving a few nanoseconds in JavaScript code.

Answer 3

1. Workbenching might result some very small differences in some cases but the way of processing is browser dependent anyway so not worth bothering
2. Because of different ways of processing
3. You can't call it a browser if the behavior would be different anyhow

Answer 4

Answering in generalities:

1. Yes, usually.
2. See Infor Here
3. Yes, because each has a different JS processing engine, however, in running a test on the site below, the Swtich always out performed the if, elseif on a large number of iterations.

Really old test site

Answer 5

A switch statement is essentially the same as a series of "if" and "else-if" statements. t's simple to use, logical in syntax.

Consider following example

var a =4 ;
if (a==1)
  alert(""+a)
else if (a==2)
  alert(""+a)
else if (a==3)
  alert(""+a)
else if (a==4)
  alert(""+a)


switch(a){
case 1:
      alert(""+a)
break
case 2:
      alert(""+a)
break
case 3:
      alert(""+a)
break
case 4:
      alert(""+a)

they both take similar execution time but switch-case looks more developer friendly.

Answer 6

Other than syntax, a switch can be implemented using a tree which makes it O(log n), while a if/else has to be implemented with an O(n) procedural approach. More often they are both processed procedurally and the only difference is syntax, and moreover does it really matter -- unless you're statically typing 10k cases of if/else anyway?

Answer 7

Sometimes it's better to use neither. For example, in a "dispatch" situation, Javascript lets you do things in a completely different way:

function dispatch(funCode) {
  var map = {
    'explode': function() {
      prepExplosive();
      if (flammable()) issueWarning();
      doExplode();
    },

    'hibernate': function() {
      if (status() == 'sleeping') return;
      // ... I can't keep making this stuff up
    },
    // ...
  };

  var thisFun = map[funCode];
  if (thisFun) thisFun();
}

Setting up multi-way branching by creating an object has a lot of advantages. You can add and remove functionality dynamically. You can create the dispatch table from data. You can examine it programmatically. You can build the handlers with other functions.

There's the added overhead of a function call to get to the equivalent of a "case", but the advantage (when there are lots of cases) of a hash lookup to find the function for a particular key.

Answer 8

The performance difference between a switch and if...else if...else is small, they basically do the same work. One difference between them that may make a difference is that the expression to test is only evaluated once in a switch while it's evaluated for each if. If it's costly to evaluate the expression, doing it one time is of course faster than doing it a hundred times.

The difference in implementation of those commands (and all script in general) differs quite a bit between browsers. It's common to see rather big performance differences for the same code in different browsers.

As you can hardly performance test all code in all browsers, you should go for the code that fits best for what you are doing, and try to reduce the amount of work done rather than optimising how it's done.