The way a browser console operates is the reason for the behavior you are witnessing.
When evaluating code, the console attempts to return a value. Simple expressions like 2 + 2 are straightforward and would likely return 4.
However, for more complex code with multiple statements, the console's behavior becomes much more intricate as it tries to make intelligent decisions. Complicating things further is the lack of standardization in console behavior, meaning what we see in one browser at one point may not hold true for another browser or a later release of the same one.
Let's delve into what's happening:
j = 0;
while (j < 3) {
j++;
}
In this code snippet, the browser attempts to discern the latest expression and outputs its value, which in this case is j++;. The returned value is 2 because that was the value of j before the loop ended since postfix increment returns the current value before changing it.
If we modify it to
j = 0;
while (j < 3) {
++j;
}
The output will be 3 for the same reasoning.
Now, let's consider something else:
j = 0;
while (j < 3) {
j++;
a = 42;
}
This will result in 42 being displayed since a = 42 is the most recent expression in the code.
j = 0;
while (j < 3) {
j++;
var a = 42;
}
For this example, it will again return 2, as the console chooses to ignore the assignment statement and focuses on the last expression.
To conlude, this behavior is not uniform across browsers, and they strive to provide some output even if it might not align with your expectations. It's best not to rely on implicit console output and instead use console.log() explicitly when you need to obtain a result.