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

Answer 1

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.