PaulUithol/Backbone-relational

previous attributes broken when another attributes changed in handler.

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#485 opened on Aug 18, 2014

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 (0 comments) (0 reactions) (0 assignees)JavaScript (2,343 stars) (344 forks)batch import
bughelp wanted

Description

Scenario:

  • has model with several listeners on some property propA
  • one of the listener change another property propB.
  • In rest of handlers for propA previousAttributes contains new value of propA instead old one.

In case of usage regular Model instead of RelationalModel previousAttributes contains old value as expected.

sample: http://jsfiddle.net/4ohq1tho/1

this cause several issues like https://github.com/kmalakoff/knockback/issues/121

Contributor guide

Tech stack
javascript
Domain
frontend
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
needs investigation
Prerequisites
Backbone model event handlingJavaScript event loop
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
Investigate the order of change event handlers in Backbone relational vs Backbone.Model. The issue is that when multiple listeners on propertyA exist, and one changes propertyB, subsequent listeners see the new value of propertyA in `previousAttributes`. Look into the Backbone source code for `change` event propagation and how RelationalModel overrides it. Compare with the regular Backbone.Model behavior. The jsfiddle provides a reproduction. Focus on the `set` method and how `previousAttributes` is stored before triggering events. Potentially modify the RelationalModel's set method to preserve the original previousAttributes across handler calls.