无法独立管理数组中的对象

Question

I'm working on a text editor using React and I want to keep track of the changes in an array. Whenever I make changes an object is added to the array (as it should) but all the other objects change as well and become the same as the new one. I'm aware of how Javascript doesn't store objects in independent variables if not reassigned so I used the spread operator to create a new array and then add a new object using Object.assign() but it's still not working and I can't figure out what I'm doing wrong.

 getNewChangesHistory(update, oldChangesHistory){ var newChangesHistory = [...oldChangesHistory, Object.assign({}, update)]; if(newChangesHistory.length > 25){ delete(newChangesHistory[26]); } return newChangesHistory; } updateDocumentContent(content){ var newDocument = {...this.state.document}; newDocument.content = content; this.setState(prevState => {return { document: newDocument, changesHistory: this.getNewChangesHistory(content, prevState.changesHistory), hasChanges: true }}) } updateTextbox(editedProperties, key){ const newDocumentContent = {...this.state.document.content}; newDocumentContent.textboxes[key] = { //Textboxes are stored as objects of an array ...editedProperties, id: key } this.updateDocumentContent(newDocumentContent) } render(){ return( <TextBox onEdit={(editedProperties) => {this.updateTextbox(editedProperties, 0)}} /> ) }

Answer 1

The problem is in updateTextbox . With {...this.state.document.content} it only creates a shallow copy. In this copy the textboxes property will still reference the same object. And you mutate that object by the assignment to its [key] property. So that mutation will be seen in all objects that have that same textboxes object reference.

One way to get rid of this, is to treat textboxes as immutable, and do this:

updateTextbox(editedProperties, key){
  const {content} = this.state.document;
  const newDocumentContent = {
    ...content,
    // create a new textboxes array
    textboxes: Object.assign([], content.textboxes, {
      [key]: {
        ...editedProperties,
        id: key
      }
    })
  };
  this.updateDocumentContent(newDocumentContent);
}