Javascript apply methods from one object to another

Question

I have been at this for hours and just can't get it quite right. I have an object with methods that works fine. I need to save it as a string using JSON.stringify and then bring it back as an object and still use the same methods.

function Workflow(){
  this.setTitle = function(newtitle){this.title = newtitle; return this;};
  this.getTitle = function(){return this.title;}; 
}

function testIn(){
  var workflow = new Workflow().setTitle('Workflow Test'); 
  Logger.log(workflow);//{title=Workflow Test}
  Logger.log(workflow.getTitle()); //Workflow Test

  var stringy = JSON.stringify(workflow);
  var newWorkflow = Utilities.jsonParse(stringy);
  Logger.log(newWorkflow); //{title=Workflow Test} 
                           //Looks like the same properties as above

  Logger.log(newWorkflow.getTitle());//Error can't find getTitle
}

I think I should prototype the new object but nothing seems to work. Please help I have very little hair left.

Possible duplicate: http://stackoverflow.com/q/6754919/902654 — someone, Sep 26 '11 at 23:42

score 1 · Answer 1 · answered Sep 26 '11 at 23:39

1

You need to copy the method to the new object:

newWorkflow.getTitle = workflow.getTitle;

answered Sep 26 '11 at 23:39

SLaks

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1

Ok but there are a lot of methods. I could do a loop newWorkflow[method] = workflow[method]; is that an option? – James Ferreira Sep 26 '11 at 23:45

score 0 · Answer 2 · answered Sep 26 '11 at 23:51

0

you are losing your functions when you stringify and parse. if you have access to jquery, the $.extend is handy (if not, just copy&paste form jquery source)

here's a demo: http://jsfiddle.net/VPfLc/

answered Sep 26 '11 at 23:51

karnyj

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9
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I so wish I had access to jquery but this is Google Apps Script which does not allow it and I have to save the object to a cell in a spreadsheet. – James Ferreira Sep 26 '11 at 23:53
just copy and paste from jquery source, its not a big function – karnyj Sep 27 '11 at 08:02

score 0 · Answer 3 · answered Sep 26 '11 at 23:57

Serializing to JSON won't store executable code. It's being removed from your object when calling JSON.stringify. Your best bet is to make the object so it can be initialized when created.

function Workflow(){
  this.initialize = function(properties) { this.title = properties.title; }
  this.setTitle = function(newtitle){this.title = newtitle; return this;};
  this.getTitle = function(){return this.title;}; 
}

function testIn(){
  var workflow = new Workflow().setTitle('Workflow Test'); 
  Logger.log(workflow);//{title=Workflow Test}
  Logger.log(workflow.getTitle()); //Workflow Test

  var stringy = JSON.stringify(workflow);
  var newWorkflow = new Workflow().initialize(Utilities.jsonParse(stringy));
  Logger.log(newWorkflow); //{title=Workflow Test} 
                           //Looks like the same properties as above

  Logger.log(newWorkflow.getTitle());//Error can't find getTitle
}

Unfortunately you don't have jQuery.extend() to automatically add properties to your object in the initialize function but you can at least add them by hand here and retain much of the same code flow you started with. — funwhilelost, Sep 26 '11 at 23:58

J. Holmes · Answer 4 · 2011-09-27T15:14:11.033

All you have to do is use call.

Workflow.call(newWorkflow);

EDIT:

If your actual Workflow() implementation sets any attributes to default values during its initilization then calling on your new json object will also reset those. Which is what I'm assuming is going on, without being able to look at your actual implementation code.

If that is the case, then you have two options.

1) Rather than blindly initilize your object (and assuming its empty), conditionally initilize your variables.

function Workflow(){
  this.setTitle = function(newtitle){this.title = newtitle; return this;};
  this.getTitle = function(){return this.title;}; 
  this.array = this.array || [];
}

for new empty objects. this.array will be null, and it'll be set to a new array. calling Workflow on a existing object that already has that property, it'll leave it alone.

2) Extract your methods into an Extension Module

function Workflow(){
  this.array = this.array || [];
  // Other work

  // Lastly include my method extensions.
  WorkflowMethodExtensions.call(this);
}

function WorkflowMethodExtensions(){
  this.setTitle = function(newtitle){this.title = newtitle; return this;};
  this.getTitle = function(){return this.title;}; 
}

Then use:

WorkflowMethodExtensions.call(newWorkflow);

to extend an existing object with those methods defined in the existion

Sooo close but one of the variables I have in the JSON string is an array and its content oddly gets lost after I use call. — James Ferreira, Sep 27 '11 at 01:17

Javascript apply methods from one object to another

4 Answers4