在 JavaScript 中，如果“删除”一个不存在的属性会发生什么？
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In JavaScript, what happens if "delete" a property that doesn't exist?
提问by thisissami
What happens in JavaScript if I have a variable, say:
如果我有一个变量，JavaScript 会发生什么，比如：
var exampleObject = {one:'foo',two:'bar'};
and then I delete a property that doesn't exist, a la:
然后我删除了一个不存在的属性，a la：
delete exampleObject.seven;
Is there a standard course of action that takes place everywhere (nothing, error message, script crashes, etc.), or is this dependent on some kind of implementation (browser engine, etc.)?
是否存在随处可见的标准操作过程（无、错误消息、脚本崩溃等），或者这是否依赖于某种实现（浏览器引擎等）？
采纳答案by user2246674
Nothing happens.
没发生什么事。
Assuming, x = {}, Type(x.y)is nota Reference Specifcation Type(there cannot be a "reference" to a property that does not exist). According to 11.4.1 The delete Operator, this satisfies the rule:
假设，x = {}，Type(x.y)是不是一个参考Specifcation类型（不可能有一个“参考”来表示不存在的属性）。根据11.4.1 删除操作符，这满足规则：
- Let ref be the result of evaluating UnaryExpression.
- If Type(ref) is not Reference, return true.
- ...
- 让 ref 为计算 UnaryExpression 的结果。
- 如果 Type(ref) 不是 Reference，则返回 true。
- ...
This behavior (of "no action") has existed for a long time - any environment that behaves differently is non-compliant. From the 3rd Edition ECMAScript Specification:
这种行为（“无行动”）已经存在很长时间了——任何行为不同的环境都是不合规的。从第三版 ECMAScript 规范：
When the [[Delete]] method of O is called with property name P, the following steps are taken:
- If O doesn't have a property with name P, return true.
- ..
当使用属性名P调用O的[[Delete]]方法时，采取如下步骤：
- 如果 O 没有名为 P 的属性，则返回 true。
- ..
回答by kennebec
If exampleObject is an object, the return value from delete is true, even if the property does not exist.
如果 exampleObject 是一个对象，则 delete 的返回值为true，即使该属性不存在。
