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"