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The in operator returns true if the specified property is in the specified object.
Syntax
propNameOrNumber in objectName
Parameters
| Parameter | Description |
|---|---|
| propNameOrNumber | A string or numeric expression representing a property name or array index. |
| objectName | Name of an object. |
Description
The following examples show some uses of the in operator.
Using in with deleted or undefined properties
If you delete a property with the delete operator, the in operator returns false for that property.
If you set a property to undefined but do not delete it, the in operator returns true for that property.