Javascript 使用 CoffeeScript 检查对象中是否存在键的最简单方法
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Simplest way to check if key exists in object using CoffeeScript
提问by ajsie
In CoffeeScript, what is the simplest way to check if a key exists in an object?
在 CoffeeScript 中，检查对象中是否存在键的最简单方法是什么？
回答by Trevor Burnham
key of obj
This compiles to JavaScript's key in obj. (CoffeeScript uses ofwhen referring to keys, and inwhen referring to array values: val in arrwill test whether valis in arr.)
这将编译为 JavaScript 的key in obj. （CoffeeScriptof在引用键和in引用数组值时使用：val in arr将测试是否val在arr.）
thejh's answer is correct if you want to ignore the object's prototype. Jimmy's answer is correct if you want to ignore keys with a nullor undefinedvalue.
如果你想忽略对象的原型，thejh 的答案是正确的。如果您想忽略带有 anull或undefined值的键，Jimmy 的回答是正确的。
回答by limscoder
The '?' operator checks for existence:
这 '？' 操作员检查是否存在：
if obj?
# object is not undefined or null
if obj.key?
# obj.key is not undefined or null
# call function if it exists
obj.funcKey?()
# chain existence checks, returns undefined if failure at any level
grandChildVal = obj.key?.childKey?.grandChildKey
# chain existence checks with function, returns undefined if failure at any level
grandChildVal = obj.key?.childKey?().grandChildKey
回答by thejh
obj.hasOwnProperty(name)
(to ignore inherited properties)
（忽略继承的属性）
