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backbone.compute.js
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backbone.compute.js
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// Backbone.Compute, v0.0.1
// Copyright (c)2012 Derick Bailey, Muted Solutions, LLC.
// Distributed under MIT license
// http://github.com/derickbailey/backbone.compute
Backbone.Compute = (function(Backbone, _){
// Model Initializer
// -----------------
//
// Initializes all of the computed fields for your
// model. Call `Backbone.Compute(this);` from within your
// model's `initialize` function.
function initializeModel(obj){
for(var field in obj){
var computeAttr = obj[field];
if (computeAttr && computeAttr.fields && computeAttr.compute){
obj[field] = computeField(field, computeAttr.fields, computeAttr.compute);
obj[field].call(obj);
}
}
}
// Computed Field Definition And Handler
// -------------------------------------
//
// Handles both the definition and execution of
// computed fields on models.
//
// The `fieldName` parameter is the name of the field
// to `set` in your model, when the dependent fields change
// and the computed field value is calculated
//
// The `fieldList` parameter can either be a single
// string, or an array of strings, representing the
// fields on which this computed field relies.
//
// The `callback` parameter is the computed field
// calculator function. This callback recieves a
// `fields` parameter. It is an object iteral that
// contains the name/value pairs for the fields that
// this computed field depends on.
function computeField(fieldName, fieldList, callback){
fieldList = _.flatten([fieldList]);
var length = fieldList.length;
var fireCallback = function(){
var fields = {};
for (var i = 0; i<length; i++){
var field = fieldList[i];
fields[field] = this.get(field);
}
var value = callback.call(this, fields);
this.set(fieldName, value);
return value;
};
var computedFunc = function(){
var cb = _.bind(fireCallback, this);
for (var i = 0; i<length; i++){
var field = fieldList[i];
this.on("change:" + field, cb);
}
return cb();
};
computedFunc.computedField = true;
return computedFunc;
}
// The raw API for computed fields. Determines whether
// you are attempting to initialize the model or define
// a computed field, and call the correct behavior.
var Compute = function(model){
return initializeModel(model);
};
return Compute;
})(Backbone, _);