Most efficient way to concatenate strings in JavaScript?

Seems based on benchmarks at JSPerf that using += is the fastest method, though not necessarily in every browser.

For building strings in the DOM, it seems to be better to concatenate the string first and then add to the DOM, rather then iteratively add it to the dom. You should benchmark your own case though.

(Thanks @zAlbee for correction)

I have no comment on the concatenation itself, but I'd like to point out that @Jakub Hampl's suggestion:

For building strings in the DOM, in some cases it might be better to iteratively add to the DOM, rather then add a huge string at once.

is wrong, because it's based on a flawed test. That test never actually appends into the DOM.

This fixed test shows that creating the string all at once before rendering it is much, MUCH faster. It's not even a contest.

(Sorry this is a separate answer, but I don't have enough rep to comment on answers yet.)