I'm trying to figure out how the setting of a property is being intercepted in jsdom's CSSStyleDeclaration implementation. This is being done for validation purposes. I want to know where this validation is happening. github link

This is the line where the setting is happening. this[lowercaseName] = value;

I'm only aware of one method that can be used to intercept this action. Which is usage of Proxy Object. But the object in question is not a proxy object.

Hence Question: What are the other ways of intercepting(man in the middle) the action of setting properties on an object?

To confirm interception is happening:

const {CSSStyleDeclaration} = require('cssstyle')
const decl = new CSSStyleDeclaration()

decl.setProperty('background-color', 'invalid-value')

decl.getPropertyValue('background-color') // '' returns empty string

decl.setProperty('background-color', '#333')

decl.getPropertyValue('background-color') // '#333'

Use can use this IDE

CodePudding user response：

What are the other ways of intercepting(man in the middle) the action of setting properties on an object?

Setters!

The set syntax binds an object property to a function to be called when there is an attempt to set that property.

In your particular example the colour validation is done by a parseColor function called by the background-color setter.