在JavaScript中是否存在null-coalescing（Elvis）运算符或安全导航运算符？ [英] Is there a null-coalescing (Elvis) operator or safe navigation operator in javascript?

问题描述

我会用例子来解释：

Elvis Operator（？：）

猫王操作员是Java三元运算符的缩短
。如果表达式解析为false或
null，
返回一个'合理的默认'值
，这是非常方便的一个
实例。一个简单的例子可能如下所示：

  def gender = user.male ？ male：female//传统的三元运算符用法
 
 def displayName = user.name？：Anonymous//更简洁的Elvis操作符
  

安全导航操作员（？。）

使用
来避免NullPointerException。
通常，当您有一个对象的引用时，您可能需要在访问对象的
方法或属性之前验证
是否为空。
为避免这种情况，安全导航
操作符将简单地返回空
，而不是抛出一个异常，如
如此：

  def user = User.find（admin）//如果'admin'不存在，则可能为空
 def streetName = user？.address？.street // streetName将会为null，如果user或user.address为null  - 没有NPE抛出
  

例如 displayname = user.name || 匿名。

但是Javascript目前没有其他功能。如果您需要其他语法，建议您查看 CoffeeScript 。它有一些简写，类似于你正在寻找的。

例如存在的操作符

  zip = lottery.drawWinner？（）。address？.zipcode 
  

功能快捷键

 （） - > //相当于function（）{} 
  

性感函数调用

  func'arg1'，'arg2'//相当于func（'arg1'，'arg2'）
  pre> 
 
 
还有多行注释和类。很明显，你必须将它编译为javascript或者以< script type ='text / coffeescript>'的形式插入页面，但它增加了很多功能:)。使用< script type ='text / coffeescript'> 实际上仅用于开发而非生产。
 
I'll explain by example:

Elvis Operator (?: )

  
The "Elvis operator" is a shortening
  of Java's ternary operator. One
  instance of where this is handy is for
  returning a 'sensible default' value
  if an expression resolves to false or
  null. A simple example might look like
  this:


def gender = user.male ? "male" : "female"  //traditional ternary operator usage

def displayName = user.name ?: "Anonymous"  //more compact Elvis operator



  
Safe Navigation Operator (?.)
  
  
The Safe Navigation operator is used
  to avoid a NullPointerException.
  Typically when you have a reference to
  an object you might need to verify
  that it is not null before accessing
  methods or properties of the object.
  To avoid this, the safe navigation
  operator will simply return null
  instead of throwing an exception, like
  so:


def user = User.find( "admin" )           //this might be null if 'admin' does not exist
def streetName = user?.address?.street    //streetName will be null if user or user.address is null - no NPE thrown

解决方案
You can use the logical 'OR' operator in place of the Elvis operator:

For example displayname = user.name || "Anonymous" .  

But Javascript currently doesn't have the other functionality.  I'd recommend looking at CoffeeScript if you want an alternative syntax.  It has some shorthand that is similar to what you are looking for.

For example The Existential Operator
zip = lottery.drawWinner?().address?.zipcode
Function shortcuts
()->  // equivalent to function(){}
Sexy function calling
func 'arg1','arg2' // equivalent to func('arg1','arg2')
There is also multiline comments and classes.  Obviously you have to compile this to javascript or insert into the page as <script type='text/coffeescript>' but it adds a lot of functionality :) .  Using <script type='text/coffeescript'> is really only intended for development and not production.

                        
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