javascript - JavaScript中是否有“空合并”运算符？(Is there a “null coalescing” operator in JavaScript?)

Question

Is there a null coalescing operator in Javascript?(Javascript中是否有空合并运算符？)

For example, in C#, I can do this:(例如，在C＃中，我可以这样做：) String someString = null; var whatIWant = someString ?? "Cookies!"; The best approximation I can figure out for Javascript is using the conditional operator:(我可以为Javascript找到的最佳近似是使用条件运算符：) var someString = null; var whatIWant = someString ? someString : 'Cookies!'; Which is sorta icky IMHO.(恕我直言，这有点棘手。) Can I do better?(我可以做得更好吗？)   ask by Daniel Schaffer translate from so

Answer 1

The JavaScript equivalent of the C# null coalescing operator ( ?? ) is using a logical OR ( || ):(与C＃空合并运算符（ ?? ）等效的JavaScript使用逻辑OR（ || ）：)

var whatIWant = someString || "Cookies!"; There are cases (clarified below) that the behaviour won't match that of C#, but this is the general, terse way of assigning default/alternative values in JavaScript.(在某些情况下（如下所述），该行为与C＃的行为不匹配，但这是在JavaScript中分配默认/替代值的通用，简洁的方法。) Clarification(澄清度) Regardless of the type of the first operand, if casting it to a Boolean results in false , the assignment will use the second operand.(无论第一个操作数的类型如何，如果将其强制转换为Boolean都将导致false ，则赋值将使用第二个操作数。) Beware of all the cases below:(当心以下所有情况：) alert(Boolean(null)); // false alert(Boolean(undefined)); // false alert(Boolean(0)); // false alert(Boolean("")); // false alert(Boolean("false")); // true -- gotcha! :) This means:(这意味着：) var whatIWant = null || new ShinyObject(); // is a new shiny object var whatIWant = undefined || "well defined"; // is "well defined" var whatIWant = 0 || 42; // is 42 var whatIWant = "" || "a million bucks"; // is "a million bucks" var whatIWant = "false" || "no way"; // is "false"