Some remark:

Replace:
.replace(from, to) - 65ms
.split(from).join(to) - 200ms

array creating is not very fast.

Work with comma separated value:
var a = b.split(','); for(var i = 0; i < a.length; i++){} - 147ms
b.replace(/[^,]+/g, function(s){}) - 235ms

But lambda expression is even worse.

Replace for the first occurrence
.replace(/s/, '') - 29ms
.replace('s', '') - 34ms

Maybe because every time called toString

Substring:
.slice - 28ms
.substr - 30ms

slice seems as better choice for string reduction.

Trim:
.replace(/^\s+|\s+$/g, '') - 64ms
.replace(/^\s+/, '').replace(/\s+$/, '') - 82ms

Get symbol from string
str[1] - 14ms
str.charAt(1) - 16ms

...

Cool. :] Good to know.
I've never really used slice much.

Usefull, thanks for that.

What surprise me was the call to replace using regex was faster than using string.
29ms vs 34ms!