javascript string string optimization problem_javascript skills

The result is not like the general saying, using array will be faster. In ie9,8. I tested it under IE core browsers such as ff, Google, Sogou, etc. It is true that the array method is slower than the " " method in tests with a magnitude of more than 100,000.
Results of 1000000 times
First time on ie (probably, ie can’t copy it, so the picture won’t be cut off)

ie maybe the memory is not recycled and a warning will pop up at the second point. And the time used is 1400 and 1200. After clicking more several times, the time of = connection method returns to 400. Is it possible that the array object is not recycled? Open the task manager and refresh the IE browser again. The memory has dropped by more than 100 MB. You should study the JavaScript memory recycling mechanism of IE.
ff

google (cannot copy data)
array time 200
str Connection time 100
opera
time 1: 1312102258270
time 2 1312102258460
time 3 1312102258592
array time 190
str connection time 132
By the way, in After the data reaches 5000000, ff throws an exception. It should be a memory overflow. . . (ps, I don’t understand very well)
Error: uncaught exception: 8.375396749959738e-274
When tested under IE, a decisive warning appears, and then out of memory.
Of course, large data connections are impossible to appear on current web pages, and data processing should be done in the background. The teacher’s host does not dare to install so many browsers
In fact, it is the jion of array, which is too time-consuming. Without adding this sentence, opera and Google show the advantages of array:
opera results:

google
array time 17
str connection time 100
Go and check the jion mechanism before writing it.
ps: browser version
google12.0.742.122
ff5.0.1
opera11.50
ie8.0.6001.18702
pss: ie processing speed is not good