JavaScript中的字符串括号

Question

I was reading Marionette's source code and I came across something like:

if (_.isObject(message)) {
    message = (
      message.prev + ' is going to be removed in the future. ' +
      'Please use ' + message.next + ' instead.' +
      (message.url ? ' See: ' + message.url : '')
    );
}

Why exactly is message wrapped in parentheses? What does that do?

Answer 1

In this specific example, the outer parentheses do not serve any function, other than (arguably) improving readability.

This code is functionally identical:

if (_.isObject(message)) {
    message = 
        message.prev + ' is going to be removed in the future. ' +
        'Please use ' + message.next + ' instead.' +
        (message.url ? ' See: ' + message.url : '');
}

The parentheses around the ternary operator are added so the ternary operator doesn't evaluate everything before the message.url .

Answer 2

I don't think the outer-most does anything. Probably the author used it for readability reasons. The inner is needed for the conditional (?) operator.

Answer 3

It's mainly for readability.
With or without, the functionality does not change.