Javascript and / or Assignment Operators

Question

I was looking at some compiled coffee code script, and I noticed something like the following, which in my opinion was really strange:

var current, x = 8; current = this._head || (this._head = x); 

after doing this, the current has a value of 8. Judging by the fact that || the boolean operator works, I would expect it to evaluate the left side first. Having received "undefined" on the left side, it moves to the right, where it assigns this._head to 8. Then it returns true, but is this part not so important? I don’t see how it can return and affect the “current” variable? Any help would be appreciated, thanks!

Answer 1

Operator || returns a value, not true . Maybe it helps to say that

 current = this._head || (this._head = x) 

can also be written as

 current = this._head ? this._head : (this._head = x); 

or

 current = this._head; if(!current) current = this._head = x; 

Answer 2

• Operator || returns the left side if it is "true", otherwise - on the right side - regardless of its likelihood. It does not pass the expression to the boolean true / false!
  • undefined || (this._head = x) undefined || (this._head = x) returns the right side
• The assignment operator also returns a value!
  • this._head = x returns 8 in the above example
• The first assignment operator assigns the value 8 to the current variable

Answer 3

You can use expresion

 var current=this._head ? this._head : (this._head = x);