Thursday, October 13, 2011

Lazy Evaluation


var boolV = true || false || true || false || true;
 console.log(boolV); //output is true

Question is did all the operations (logical) got executed ?
Ans is NO.

If several logical operations one after the other, but the result becomes clear at some point before the end of entire operation, then the remaining operations are not performed.

Lets consider the above statement.

var boolV = true || false || true || false || true;

It is before the first local operation it is clear that boolV is  suppose to have value true irrespective of any logical or operation. hence the other logical operations are not executed. in the above statement.

To verify this, we will the following code.

var a =10;
console.log(a); //output 10
console.log(!!++a); //output true
console.log(a);        //output 11
var boolV = true || false || true || false || true || !!++a;
console.log(boolV);  //output true
console.log(a);         //output 11 (which imples the !!++a didn't got executed)
boolV =  !!++a || true || false || true || false || true ;
console.log(boolV); //output true
console.log(a);        //output 12 (which imples the !!++a  got executed)


Ain't that interesting !!!

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