This is a one-line shorthand for an if-else statement.(这是if-else语句的单行简写。)
It's called the conditional operator.(它称为条件运算符。) 1(1个)
Here is an example of code that could be shortened with the conditional operator:(这是可以通过条件运算符缩短的代码示例：)
var userType;
if (userIsYoungerThan18) {
userType = "Minor";
} else {
userType = "Adult";
}
if (userIsYoungerThan21) {
serveDrink("Grape Juice");
} else {
serveDrink("Wine");
}
This can be shortened with the ?: like so:(可以使用?:来缩短它，就像这样：)
var userType = userIsYoungerThan18 ? "Minor" : "Adult";
serveDrink(userIsYoungerThan21 ? "Grape Juice" : "Wine");
Like all expressions, the conditional operator can also be used as a standalone statement with side-effects, though this is unusual outside of minification:(与所有表达式一样，条件运算符也可以用作具有副作用的独立语句，尽管在缩小之外这是不常见的：)
userIsYoungerThan21 ? serveGrapeJuice() : serveWine();
They can even be chained:(它们甚至可以链接：)
serveDrink(userIsYoungerThan4 ? 'Milk' : userIsYoungerThan21 ? 'Grape Juice' : 'Wine');
Be careful, though, or you will end up with convoluted code like this:(但是要小心，否则最终将得到如下复杂的代码：)
var k = a ? (b ? (c ? d : e) : (d ? e : f)) : f ? (g ? h : i) : j;
1 Often called "the ternary operator," but in fact it's just a ternary operator [an operator accepting three operands].(1 通常称为“三元运算符”，但实际上它只是一个三元运算符[一个接受三个操作数的运算符]。) It's the only one JavaScript currently has, though.(不过，这是目前唯一的JavaScript。) 与恶龙缠斗过久,自身亦成为恶龙；凝视深渊过久,深渊将回以凝视…
