Are there legitimate uses for JavaScript's “with” statement?

Question

Alan Storm\'s comments in response to my answer regarding the with statement got me thinking. I\'ve seldom found a reason to use this particular language feature, and had ne

Answer 1

As my previous comments indicated, I don't think you can use with safely no matter how tempting it might be in any given situation. Since the issue isn't directly covered here, I'll repeat it. Consider the following code

user = {};
someFunctionThatDoesStuffToUser(user);
someOtherFunction(user);

with(user){
    name = 'Bob';
    age  = 20;
}

Without carefully investigating those function calls, there's no way to tell what the state of your program will be after this code runs. If user.name was already set, it will now be Bob. If it wasn't set, the global name will be initialized or changed to Bob and the user object will remain without a name property.

Bugs happen. If you use with you will eventually do this and increase the chances your program will fail. Worse, you may encounter working code that sets a global in the with block, either deliberately or through the author not knowing about this quirk of the construct. It's a lot like encountering fall through on a switch, you have no idea if the author intended this and there's no way to know if "fixing" the code will introduce a regression.

Modern programming languages are chocked full of features. Some features, after years of use, are discovered to be bad, and should be avoided. Javascript's with is one of them.