Best practices and gotchas with v8

Try/Catch blocks can be expensive inside functions

If you have a function that has performance critical code in it (particularly if it's allocating a lot of variables), then don't use a try/catch inside the function. Catch the errors from outside the function instead.

function test1(j) {
        try{
        	var s = 0;
        	for (var i = 0; i < j; i++) s = i;
        	for (var i = 0; i < j; i++) s = i;
        	for (var i = 0; i < j; i++) s = i;
        	for (var i = 0; i < j; i++) s = i;
        	return s;
        }
        catch(ex) {
        	console.log(ex);
        }
}

// Slow!
test1(1000000);

function test2(j) {
    var s = 0;
    for (var i = 0; i < j; i++) s = i;
    for (var i = 0; i < j; i++) s = i;
    for (var i = 0; i < j; i++) s = i;
    for (var i = 0; i < j; i++) s = i;
    return s;
}

// Much faster
try {
    test2(1000000);
} catch(ex) {
    console.log(ex);
}

See this mailing list thread for background and this performance test case.