在Java语言中使用短路评估设置字符串时出现意外行为

Question

I want to use this short-circuit evaluation to report a nice status of multiple items in an one liner. But the result is not as expected as shown below:

 var items = [{ "id": 1, "available": true }, { "id": 2, "available": false }, { "id": 3, "error": "Server not found for that TLD" }]; items.forEach(function(item) { console.log(item.id, item.error || item.available ? "Available" : "Not available"); }); 

This produced the following log:

1 "Available"
2 "Not available"
3 "Available"

At 3 I expected it to show the error because item.error is a string and should evaluate to `true, why does it skip it to item.available?

Answer 1

item.error || item.available item.error || item.available is truthy.

You need parentheses:

item.error || (item.available ? "Available" : "Not available")

Answer 2

As @SLaks said parentheses will fix the problem. The order of operations is different than you expected. The || is evaluated before the ternary operator.

You can see the order here. Logical OR is just above the conditional operator https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Operator_Precedence