Chrome's JavaScript Console Behavior: Evaluating Objects Lazily

The behavior of the Chrome JavaScript console when evaluating objects has been observed as potentially unexpected. To illustrate this, consider the following code:

var s = ["hi"];
console.log(s);
s[0] = "bye";
console.log(s);

In Firefox, the console outputs:

[ "hi" ]
[ "bye" ]

[ "bye" ]
[ "bye" ]

This behavior suggests that Chrome's console may be "lazy" when evaluating objects. When the first console.log statement is executed, the console references the object in memory. Any subsequent modifications to the object, such as changing the first element from "hi" to "bye," are not reflected in the output of the first console.log statement. This implies that the console only evaluates the object at the time of the first console.log statement and stores the snapshot.

This behavior is documented in the following Webkit bug report: https://bugs.webkit.org/show_bug.cgi?id=35801 (now fixed). The bug states that Chrome's console does not perform lazy evaluation for objects that are accessed directly, resulting in the observed behavior.

[ "hi" ]
[ "bye" ]

To prevent this unexpected behavior, one can call toString on the object before passing it to console.log. This forces Chrome to create a representation of the object that is not altered by subsequent changes, ensuring that the console output reflects the current state of the object.

hi
bye

Output: