Reflect: Reflect.defineProperty()

Reflect.defineProperty() is like Object.defineProperty() but returns a Boolean.

the function itself

• is static on the Reflect object
• is of type function

the 1st parameter is the object on which to define a property

• fails if it is not an object
• accepts an object
• accepts an instance (of a class)

2nd parameter is the name of the property to be defined on the object (normally a string)

• works with a normal string
• a number gets converted into a string
• undefined also gets converted into a string (watch out!)
• it can be a symbol

the value is part of the 3rd parameter, given as a property in an object {value: ...}

• contains the initial value of the property, as an object in the property value
• can be of any type (even itself)

the return value of the function indicates wether the property was defined successfully

returns true

• when the property was created (which requires the 3rd parameter too!!!)
• no matter what the value of the property is (just the 3rd param has to exist as {})

returns false

• when a non-configurable property wants to be changed to configurable=true
• when the object we want to add a property to is frozen

Links

spec The specification for this function.
docs mdn The MDN docs for this function.
announcement Announcement of this kata on twitter.