Performance difference between []+[] and [].join(',')+[].join(',')

Question

Just while fiddling through arrays i found this.

why there is significant difference between the following three statements:

[1,2]+[3,4];

[1,2].toString()+[3,4].toString();

[1,2].join(',')+[3,4].join(',');

And if [1,2]+[1,2] performs the same as converting to string and then joining the two strings, then shouldnt be performance of them be somewhat similar

This question is inspired from this answer

I'd assume because you are telling the javascript engine to convert to a string which has faster operators that a generic array that can contain any object. — abc123, Jul 13 '17 at 14:22
In all cases it's about a microsecond or less per operation. What difference does it make? It probably varies between JavaScript platforms anyway. — Pointy, Jul 13 '17 at 14:23
By the way, I'm curious how `.join()` (without the redundant argument `','`) compares. — Patrick Roberts, Jul 13 '17 at 14:24

score 4 · Accepted Answer · answered Jul 13 '17 at 14:23

It probably has something to do with implicit and explicit coercion.

For [1,2]+[3,4], the interpreter has to figure out on it's own that string is the desired output.

For both [1,2].toString()+[3,4].toString(); and [1,2].join(',')+[3,4].join(',');, you're already telling the interpreter it's working with strings.

The difference between the last 2 lines is pretty much negligible.

In the end, even if you're doing this a million times, you're not really going to notice a difference.

Performance difference between []+[] and [].join(',')+[].join(',')

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