你如何使用？：（条件）JavaScript 中的运算符？
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How do you use the ? : (conditional) operator in JavaScript?
提问by muudless
Can someone please explain to me in simple words what is the ?:(conditional, "ternary") operator and how to use it?
有人可以用简单的话向我解释什么是?:（条件，“三元”）运算符以及如何使用它？
回答by Peter Olson
This is a one-line shorthand for an if-else statement. It's called the conditional operator.1
这是 if-else 语句的单行简写。它被称为条件运算符。1
Here is an example of code that could be shortened with the conditional operator:
以下是可以使用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:
这可以用?:类似的方式缩短：
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 unusualoutside of minification:
像所有表达式一样，条件运算符也可以用作具有副作用的独立语句，尽管这在缩小之外是不寻常的：
userIsYoungerThan21 ? serveGrapeJuice() : serveWine();
They can even be chained:
它们甚至可以被链接起来：
serveDrink(userIsYoungerThan4 ? 'Milk' : userIsYoungerThan21 ? 'Grape Juice' : 'Wine');
Be careful, though, or you will end up with convoluted code like this:
不过要小心，否则你最终会得到像这样的复杂代码：
var k = a ? (b ? (c ? d : e) : (d ? e : f)) : f ? (g ? h : i) : j;
1Often called "the ternary operator," but in fact it's just aternary operator [an operator accepting three operands]. It's the only one JavaScript currently has, though.
1通常被称为“三元运算符”，但实际上它只是一个三元运算符[接受三个操作数的运算符]。不过，它是 JavaScript 目前唯一的一种。
回答by Jeffrey Roosendaal
I want to addsome to the given answers.
我想在给定的答案中添加一些内容。
In case you encounter (or want to use) a ternary in a situation like 'display a variable if it's set, else...', you can make it even shorter, without a ternary.
如果您遇到（或想使用）三元在“如果设置了变量，则显示变量，否则...”之类的情况下，您可以使其更短，而无需 ternary。
Instead of:
代替：
var welcomeMessage = 'Hello ' + (username ? username : 'guest');
You can use:
您可以使用：
var welcomeMessage = 'Hello ' + (username || 'guest');
This is Javascripts equivallent of PHP's shorthand ternary operator ?:
这是 PHP 的速记三元运算符的 Javascripts 等价物 ?:
Or even:
甚至：
var welcomeMessage = 'Hello ' + (username || something || maybethis || 'guest');
It evaluates the variable, and if it's false or unset, it goes on to the next.
它评估变量，如果它为假或未设置，则继续下一个。
回答by Michael Robinson
It's called the 'ternary' or 'conditional' operator.
它被称为“三元”或“条件”运算符。
Example
例子
The ?: operator can be used as a shortcut for an if...else statement. It is typically used as part of a larger expression where an if...else statement would be awkward. For example:
?: 运算符可用作 if...else 语句的快捷方式。它通常用作较大表达式的一部分，其中 if...else 语句会很笨拙。例如：
var now = new Date();
var greeting = "Good" + ((now.getHours() > 17) ? " evening." : " day.");
The example creates a string containing "Good evening." if it is after 6pm. The equivalent code using an if...else statement would look as follows:
该示例创建了一个包含“晚安”的字符串。如果是下午6点以后。使用 if...else 语句的等效代码如下所示：
var now = new Date();
var greeting = "Good";
if (now.getHours() > 17)
greeting += " evening.";
else
greeting += " day.";
From MSDN JS documentation.
来自MSDN JS 文档。
Basically it's a shorthand conditional statement.
基本上它是一个速记条件语句。
Also see:
另见：
回答by David Tang
It's a little hard to google when all you have are symbols ;) The terms to use are "javascript conditional operator".
当你只有符号时，用谷歌搜索有点困难;) 使用的术语是“javascript 条件运算符”。
If you see any more funny symbols in Javascript, you should try looking up Javascript's operators first: MDC's list of operators. The one exception you're likely to encounter is the $symbol.
如果您在 Javascript 中看到更多有趣的符号，您应该首先尝试查找 Javascript 的运算符：MDC 的运算符列表。您可能会遇到的一个例外是$符号。
To answer your question, conditional operatorsreplace simple if statements. An example is best:
为了回答您的问题，条件运算符替换了简单的 if 语句。一个例子是最好的：
var insurancePremium = age > 21 ? 100 : 200;
Instead of:
代替：
var insurancePremium;
if (age > 21) {
insurancePremium = 100;
} else {
insurancePremium = 200;
}
回答by Ernest Friedman-Hill
z = (x == y ? 1 : 2);
is equivalent to
相当于
if (x == y)
z = 1;
else
z = 2;
except, of course, it's shorter.
除了，当然，它更短。
回答by Arif
Most of the answers are correct but I want to add little more. The ternary operatoris right-associative, which means it can be chainedin the following way if … else-if?… else-if … else:
大多数答案是正确的，但我想补充一点。该三元运算符是右结合的，这意味着它可以被链接以下列方式if … else-if?… else-if … else：
function example() {
return condition1 ? value1
: condition2 ? value2
: condition3 ? value3
: value4;
}
Equivalent to:
相当于：
function example() {
if (condition1) { return value1; }
else if (condition2) { return value2; }
else if (condition3) { return value3; }
else { return value4; }
}
More details is here
更多细节在这里
回答by Simplans
Ternary Operator
三元运算符
Commonly we have conditional statements in Javascript.
通常我们在 Javascript 中有条件语句。
Example:
例子：
if (true) {
console.log(1)
}
else {
console.log(0)
}
# Answer
# 1
but it contain two or more lines and cannot assign to a variable. Javascript have a solution for this Problem Ternary Operator. Ternary Operator can write in one line and assign to a variable.
但它包含两行或更多行并且不能分配给变量。Javascript 有针对这个问题三元运算符的解决方案。三元运算符可以写在一行中并分配给变量。
Example:
例子：
var operator = true ? 1 : 0
console.log(operator)
# Answer
# 1
This Ternary operator is Similar in C programming language.
这个三元运算符在 C 编程语言中是相似的。
回答by eagle12
It is called the ternary operator
它被称为三元运算符
tmp = (foo==1 ? true : false);
回答by Guy Keren
Hey mate just remember js works by evaluating to either true or false, right?
嘿，伙计，请记住 js 通过评估 true 或 false 来工作，对吗？
let's take a ternary operator :
让我们拿一个三元运算符：
questionAnswered ? "Awesome!" : "damn" ;
First, js checks whether questionAnswered is trueor false.
首先，js 检查 questionAnswered 是true还是false。
if true( ?) you will get "Awesome!"
如果 true( ?) 你会得到“真棒！”
else ( :) you will get "damn";
否则 ( :) 你会得到“该死的”；
Hope this helps friend :)
希望这对朋友有帮助:)
回答by Gajendra D Ambi
x = 9
y = 8
unary
一元
++x
--x
Binary
二进制
z = x + y
Ternary
三元
2>3 ? true : false;
2<3 ? true : false;
2<3 ? "2 is lesser than 3" : "2 is greater than 3";
