CODEWITHSUNDEEP
javascript
Visconte
Visconte

Reputation: 139

How does this tricky js assignment work?

 let at = 1;
 console.log(at + - + + + - ++at);

How does this work actually? I will appreciate any help.

Upvotes: 2

Views: 63

Answers (1)

T.J. Crowder
T.J. Crowder

Reputation: 1075199

It's not as deep as you probably think it is. :-) It's just this:

console.log(at + ++at);

The series - + + + - is just a bunch of unary - and +. The + don't do anything (in this case, because they're operating on the result of ++at which is already a number), and the two - cancel each other out.

So looking at at + ++at: The binary + (addition) evaluates its left hand operand, and then its right-hand operand, and then adds them together (when both are numbers). The left-hand operand is at, which evaluates to 1; the right-hand is ++at, which increments at to 2 and takes the new value (2) as its result. So, 1 + 2 = 3.

We can make it even more confusing by removing optional whitespace, leaving only what's required to differentiate between + and ++:

console.log(at+-+ + +-++at);

...but we wouldn't do that to the people coming after us, would we? :-)

If you ever want to see the details of how an expression breaks down, the Esprima folks have a handy page showing the parsing tree of whatever you paste in: http://esprima.org/demo/parse.html

Upvotes: 10

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