Question:
While reading I found this expression:
_=$=+[],++_+''+$
Curiously, it is a valid expression in javascript , but the most curious thing is that when it is executed, the result is:
10
I tried to make sense of it by breaking the expression down but I didn't get much done.
Why is the result of that expression equal to 10 ?
Answer:
Easy, this expression
_=$=+[],++_+''+$
It can be written more readably like this
_ = $ = +[], ++_ + '' + $
Which can be understood as:
(_ = $ = +[]), (++_ + '' + $)
Which is the same as:
_ = $ = +[];
++_ + '' + $;
Which is the same as:
$ = +[];
_ = $;
++_ + '' + $;
That to read it easier we can rename variables like:
var1 = +[]; // +[] fuerza al empty array a volverse number 0
var2 = var1; // Ahora var1 y var2 valen 0
++var2 + '' + var1; // ++var2 === 1, 1 + '' === '1' y '1' + 0 === '10'
Than executing it step by step:
var1 = 0;
var2 = var1;
++var2 + '' + var1
...
var2 = 0;
++var2 + '' + var1;
...
++var2 + '' + 0; //var2 === 0
...
1 + '' + 0;
...
'1' + 0;
...
'10';