~~ Operator Javascript

Question

I came across this operator preceding a 'this' keyword in some Node.js Harmony code, specifically working with the Koa web framework.

The example code is below:

app.use(function *(){
   var n = ~~this.cookies.get('view') + 1;
   this.cookies.set('view', n);
   this.body = n + ' views';
});

A routine google search showed up nothing so I am throughly confused. The only thing I can say for certain is that it is essential to the functionality of that snippet, as the code stops working when it is removed.

Any insight would be appreciated with identifying the purpose of this alien operator.

@abligh yes, it is. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_Operators#.7E_(Bitwise_NOT) — Fabrício Matté, Jan 18 '15 at 21:24
I wasn't aware that Javascript could do bitwise logic. That may well be it, I'll write some tests to verify! — Alexander Christie, Jan 18 '15 at 21:25

score 2 · Accepted Answer · answered Jan 18 '15 at 21:25

2

It's a double bitwise-NOT. Its only practical effect (as far as I can see) is to cast its argument (all of this.cookies.get('view') in this case) as an integer.

answered Jan 18 '15 at 21:25

Malvolio

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Uh, that's what an integer is, the whole part (and the sign) of the number. – Malvolio Jan 18 '15 at 21:32
this.cookies.get() returns a String so the double bitwise appears to be needed so that you can increment the value. – Alexander Christie Jan 18 '15 at 21:47

~~ Operator Javascript

1 Answers1