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Is Chrome's JavaScript console lazy about evaluating arrays?
I have the following snippets in javascript whose output makes me feel that something is going wrong.
1.
a=2;
console.log(a);
a+=2;
console.log(a);
Output:2 4 ; as expected
2.
t=[0,2];
console.log(t);
t[0]+=2;
console.log(t);
Output: [2,2] [2,2]
Shouldn't the output be [0,2] [2,2] ? And whats the difference between the above two cases that results in the different answers in both the cases?
It's because the log is delayed until Chrome has time to do it (i.e. your scripts releases the CPU).
Try this to understand what happens :
var t=[0,2];
console.log(t);
setTimeout(function() {
t[0]+=2;
console.log(t);
}, 1000);
It outputs what you expect.
Is that a bug of Chrome ? Maybe a side effect of an optimization. At least it's a dangerous design...
Why is there a difference ? I suppose Chrome stores temporarily what it must log, as a primary (immutable) value in the first case, as a pointer to the array in the last case.
console.log in chrome/ff is asynchronous and objects that are logged are interpreted at the time when they're expanded. . Instead make a copy of the object if you want to see its value at that time (for an array):
t=[0,2];
console.log(t.slice(0));
t[0]+=2;
console.log(t);
With an array, calling .slice will duplicate the array and not create a reference. I wouldn't suggest using a time out: this really doesn't solve the problem, just circumvents it temporarily.
Everything you're doing is right, but chrome's logging is screwy/delayed. Try making a copy of the variable and adding to that and you'll see that your code is correct.
Chrome's logging is delayed in the newer versions, no problem from your end. Make a copy of the variable or use setTimeout.