Develop Reference

Changing the URL of a Request object from the Fetch API

Say if I have small function that takes a Request object as an argument, and calls the fetch() API.
Except I always want to append something to the url, such as ?foo=bar. I'm curious what the best way would be to go about that.
Example:
function fetchFoo(request) {
request.url += '?foo=bar';
return fetch(request);
}
The issue I have is that this won't work. The Fetch API specification states that the url property read-only.
Is there a way to work around this? I'm thinking I might need to construct an all-new Request object, but I'm unsure what a clever way is to inherit all the options from the previous Request object.
Note that I am able to override any other property by using this syntax:
var originalRequest = new Request('/url');
var overriddenRequest = new Request(originalRequest, { method: 'POST' });
Although it wasn't clear from the docs, it seems that the second init parameter takes precedence over the values passed via the originalRequest parameter. I just can't seem to come up with a way to do this for the url as well.

You could leverage the keys that are on the Request.prototype to build a new Request object in just a few lines.
function newRequest(input, init) {
var url = input;
if (input instanceof Request) {
url = mutateUrl(input.url);
init = init || {};
Object.keys(Request.prototype).forEach(function (value) {
init[value] = input[value];
});
delete init.url;
return input.blob().then(function (blob) {
if (input.method.toUpperCase() !== 'HEAD' && input.method.toUpperCase() !== 'GET' && blob.size > 0) {
init.body = blob;
}
return new Request(url, init);
})
} else {
url = mutateUrl(url);
}
return new Request(url, init);
}
Note the special case for body discussed in this answer.

Using Backbone Fetch Success Callback to Change Data Before Initializing View

I'm looking for a way to intercept the value returned from a server when I fetch a backbone model (a collection, strictly speaking) from the server, then modify it before continuing. I would think that I could do something like this
SessionController.prototype._initPages = function() {
return App.pages.fetch({
reset: true,
success: function(model, response, options) {
//modify the contents of response
}
};
And my modifications would be reflected in the model that's used to initialize the view.
However I was looking at the backbone source and I think I may have misunderstood something.
fetch: function(options) {
options = options ? _.clone(options) : {};
if (options.parse === void 0) options.parse = true;
var success = options.success;
var collection = this;
options.success = function(resp) {
var method = options.reset ? 'reset' : 'set';
collection[method](resp, options); //this line updates the model
if (success) success(collection, resp, options); // my success callback
collection.trigger('sync', collection, resp, options);
};
wrapError(this, options);
return this.sync('read', this, options);
}
For my needs, it seems the two commented lines need to be switched, though I assume I'm just misunderstanding how to use this feature.
How can I modify the server response before it becomes my model?

I think you could just override the parse function to modify your data as needed
http://backbonejs.org/#Model-parse

Backbone: Feed JSON in a variable instead of fetching through URL

We are trying to modify an existing script which uses backbone.js to fetch JSON from a URL and render it in a defined way on screen.
Earlier the script was pointing to an external PHP file to fetch the JSON from it.
url: function () {
var ajaxValue = document.getElementById('ajax').value;
if(ajaxValue==0){
return this.options.apiBase + '/liveEvents.json';
} else {
var eventDate = document.getElementById('timestamp').value;
return this.options.apiBase + '/ajax.php?eventDate='+eventDate;
}
},
But now we are trying to omit the requirement of PHP and get JSON purely using Javascript. For this, we created a JS function fetch_data_set(), that returns proper JSON
var ArrayMerge = array1.concat(array2,array3,array4);
return JSON.stringify(ArrayMerge);
So our question is, how can we feed this JSON to backbone instead of using an external URL. Because if we do this (which is obviously wrong):
url: function () {
var ajaxValue = document.getElementById('ajax').value;
if(ajaxValue==0){
var data_set = fetch_data_set();
return data_set;
}
},
It throws error: Error: A "url" property or function must be specified

The main key is to extend Backbone.sync instead of url() method, so you could use this way to fetch your models in any kind of model, and you could do something similar like this link:
https://github.com/huffingtonpost/backbone-fixtures/blob/master/backbone-fixtures.js

Backbone.Model contains a sync() function able to load JSON data from an url. sync() uses the url() function to determine from where it should fetch data. (Note : sync() is called under-the-hood by save(), fetch() and destroy())
The trick here is that you should stop overriding url() and reimplement sync() directly instead, cf. http://backbonejs.org/#Model-sync
Here is an example :
// specialized version to be used with a store.js - like object
sync: function(method, model, options) {
console.log("sync_to_store begin('"+method+"',...) called with ", arguments);
var when_deferred = when.defer();
var id = this.url();
if(method === "read") {
if(typeof id === 'undefined')
throw new Error("can't fetch without id !");
var data = model.store_.get(id);
// apply fetched data
model.set(data);
when_deferred.resolve( [model, undefined, options] );
}
else if(method === "create") {
// use Backbone id as server id
model.id = model.cid;
model.store_.set(id, model.attributes);
when_deferred.resolve( [model, undefined, options] );
}
else if(method === "update") {
if(typeof id === 'undefined')
throw new Error("can't update without id !");
model.store_.set(id, model.attributes);
when_deferred.resolve( [model, undefined, options] );
}
else if(method === "delete") {
if(typeof id === 'undefined')
throw new Error("can't delete without id !");
model.store_.set(id, undefined);
model.id = undefined;
when_deferred.resolve( [model, undefined, options] );
}
else {
// WAT ?
}
console.log("sync_to_store end - Current changes = ", model.changed_attributes());
return when_deferred.promise;
}
Note 1 : API is slightly different from vanilla Backbone since I return
a when promise
Note 2 : url() is still used, as an id

Exclude model properties when syncing (Backbone.js)

Is there a way to exclude certain property from my model when I sync?
For example, I keep in my model information about some view state. Let's say I have a picker module and this module just toggle a selected attributes on my model. Later, when I call .save() on my collection, I'd want to ignore the value of selected and exclude it from the sync to the server.
Is there a clean way of doing so?
(Let me know if you'd like more details)

This seems like the best solution (based on #nikoshr referenced question)
Backbone.Model.extend({
// Overwrite save function
save: function(attrs, options) {
options || (options = {});
attrs || (attrs = _.clone(this.attributes));
// Filter the data to send to the server
delete attrs.selected;
delete attrs.dontSync;
options.data = JSON.stringify(attrs);
// Proxy the call to the original save function
return Backbone.Model.prototype.save.call(this, attrs, options);
}
});
So we overwrite save function on the model instance, but we just filter out the data we don't need, and then we proxy that to the parent prototype function.

In Underscore 1.3.3 they added pick and in 1.4.0 they added omit which can be used very simply to override your model's toJSON function to whitelist attributes with _.pick or blacklist attributes with _.omit.
And since toJSON is used by the sync command for passing the data to the server I think this is a good solution as long as you do not want these fields wherever else you use toJSON.
Backbone.Model.extend({
blacklist: ['selected',],
toJSON: function(options) {
return _.omit(this.attributes, this.blacklist);
},
});

my solution combine all the above. just use white list instead of black one .. this is good rule in general
define
attrWhiteList:['id','biography','status'],
and then overwrite the save
save: function(attrs, options) {
options || (options = {});
//here is whitelist or all
if (this.attrWhiteList != null )
// Filter the data to send to the server
whitelisted = _.pick(this.attributes, this.attrWhiteList);
else
whitelisted =this.attributes;
/* it seems that if you override save you lose some headers and the ajax call changes*/
// get data
options.data = JSON.stringify(whitelisted);
if ((this.get('id') == 0) || (this.get('id') == null))
options.type = "POST"
else
options.type = "PUT";
options.contentType = "application/json";
// options.headers = {
// 'Accept': 'application/json',
// 'Content-Type': 'application/json'
// },
// Proxy the call to the original save function
return Backbone.Model.prototype.save.call(this, attrs, options);
},

In fact there is a much simpler way of achieving this without messing with backbone save or sync function since you would no be expecting this behaviour to be permanent
if you look at backbone.js line 1145 you will see that
// Ensure that we have the appropriate request data.
if (options.data == null && model && (method === 'create' || method === 'update' || method === 'patch')) {
params.contentType = 'application/json';
params.data = JSON.stringify(options.attrs || model.toJSON(options));
}
Which means that you may override the data part of the xhr by putting data in your options
Since backbone save requires model.save([attributes], [options])
But remember that attributes like id might be essential to proper saving
Example
model.save( {}, { data: JSON.stringify(data) } ) ;
So you should be doing something like this
var data = { id : model.id , otherAttributes : 'value' } ;
model.save( {}, { data : JSON.stringify(data) } );
This do the trick quite well for me and could be used with any backbone with xhr such as fetch, save, delete, ...

Based on several of the answers, this accounts for cases of null objects and a conditional in Backbone that doesn't sent the contentType if options.data is already set:
EDITABLE_ATTRIBUTES = ["name", "birthdate", "favoriteFood"];
...
save: function(attrs, options) {
// `options` is an optional argument but is always needed here
options || (options = {});
var allAttrs = _.extend({}, this.attributes, attrs);
var allowedAttrs = _.pick(allAttrs, EDITABLE_ATTRIBUTES);
// If `options.data` is set, Backbone does not attempt to infer the content
// type and leaves it null. Set it explicitly as `application/json`.
options.contentType = "application/json";
options.data = JSON.stringify(allowedAttrs);
return Backbone.Model.prototype.save.call(
this, allowedAttrs, options);
},

I found some problems with the accepted solution, as options.data modifies the way Backbone makes the calls. Better using options.attrs as this:
Backbone.Model.extend({
save: function (attrs, options) {
options = options || {};
attrs = _.extend({}, _.clone(this.attributes), attrs);
// Filter the data to send to the server
delete attrs.selected;
options.attrs = attrs;
// Proxy the call to the original save function
return Backbone.Model.prototype.save.call(this, attrs, options);
}
});

Since save uses toJSON we override it:
toJSON: function(options) {
var attr = _.clone(this.attributes);
delete attr.selected;
return attr;
},
But it may not work if you're using toJSON and need selected in views for example. Otherwise you probably need to override save method.

Set options.attrs will allow you customise api param:
var model = new Backbone.Model();
model.save(null, {
wait: true,
success: function() {
},
attrs: _.omit(model.attributes, 'selected')
});

If it is a one-off occasion, you could use mode.unset('selected', { silent:true }) (silent is set only to avoid firing the change event), to remove the attribute... This has the not so nice counter-effect of having to re-set it after saving though.
This said, I totally endorse one of the solutions above. Moreover if this is something you need on a more regular basis.

To set only desired values, use HTTP PATCH insead of HTTP POST. On the backbone side, just add a patch attribute to the save method:
entity.save(data,{patch:true})
Using save with this attribute, only fields passed as data are sent to the server.

Having this same issue, I decided to create a small module that can help : https://github.com/lupugabriel1/backbone-model-save
This is how you can use it in your models:
var myModel = new Backbone.ModelSave.extend({
notSync: ['name', 'age']
});

Backbone data mapping

For mapping my backbone models to what I get from the server I am using a technique described on the GroupOn Dev blog: https://engineering.groupon.com/2012/javascript/extending-backbone-js-to-map-rough-api-responses-into-beautiful-client-side-models/
However, this only maps incoming data to the model.
I would like this to go both ways, so that when I save a model, it prepares the models attributes to match the servers model.
What would be the best solution to prepare the output of the model?

I've run into this exact same issue where my server response is completely different from what I am able to post. I discovered within the mechanics of the Backbone.sync object a way to that I could post to my server a custom JSON object in the following statement in Backbone.sync:
if (!options.data && model && (method == 'create' || method == 'update')) {
params.contentType = 'application/json';
params.data = JSON.stringify(model.toJSON());
}
sync evaluates if options.data does not exist then sets the params.data to the stringified model. The options.data check keyed me off. If that exists, sync will use that instead of the model. So given this, I overrode my model.save so could pass in an attributes hash that my server expects.
Here's how I overrode it:
save : function(key, value, options) {
var attributes = {}, opts = {};
//Need to use the same conditional that Backbone is using
//in its default save so that attributes and options
//are properly passed on to the prototype
if (_.isObject(key) || key == null) {
attributes = key;
opts = value;
} else {
attributes = {};
attributes[key] = value;
opts = options;
}
//In order to set .data to be used by Backbone.sync
//both opts and attributes must be defined
if (opts && attributes) {
opts.data = JSON.stringify(attributes);
opts.contentType = "application/json";
}
//Finally, make a call to the default save now that we've
//got all the details worked out.
return Backbone.Model.prototype.save.call(this, attributes, opts);
}
So how do you use this in your case? Essentially what you'll do is create a method that reverses the mapping and returns the resulting JSON. Then you can invoke save from your view or controller as follows:
getReversedMapping : function() {
ver reversedMap = {};
...
return reversedMap;
},
saveToServer : function() {
this._model.save(this.getReverseMapping, {
success : function(model, response) {
...
},
error : function(model, response) {
...
}
})
}
Since your overridden save automatically copies the JSON you pass in to options.data, Backbone.sync will use it to post.

The answer by Brendan Delumpa works, but it over-complicates things.
Don't do this in your save method. You don't want to copy over these parameter checks each time (and what if they somehow change in Backbone?).
Instead, overwrite the sync method in your model like this:
var MyModel = Backbone.Model.extend({
...,
sync: function (method, model, options) {
if (method === 'create' || method === 'update') {
// get data from model, manipulate and store in "data" variable
// ...
options.data = JSON.stringify(data);
options.contentType = 'application/json';
}
return Backbone.Model.prototype.sync.apply(this, arguments);
}
});
That's all there is to it when you need to "prepare" the data in a server-ready format.