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

Answering in generalities:

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

Test site

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.

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.