I have the following code:
MyUser.find().then(function (res) {
console.log(res[0]);
});
This effectively logs a model instance, which is fine. However, if I try to do this:
MyUser.find().then(function (res) {
delete res[0].name;
console.log(res[0]);
});
This delete statement doesn't work. Anyone knows why?
You did not provide any detail about the elements of the res array, but here is a possible cause.
Properties added to an Object using Object.defineProperty(obj, prop, descriptor) are, by default, immutable. Specifically, the descriptor property configurable, which defaults to false, determines whether the property is deletable.
Related
There are no details about isFile() function in documentation of fs.Stats class
How it works? What exactly it checks?
At the OS level an entry for a given entry is marked as either a file or a directory entry. That information does not appear to be directly surfaced in the fs.Stats data structure, but it is something that the isFile() method can tell from the fs.Stats data structure.
By looking at the code for fs.js in node.js, you can see these:
fs.Stats.prototype._checkModeProperty = function(property) {
return ((this.mode & constants.S_IFMT) === property);
};
fs.Stats.prototype.isFile = function() {
return this._checkModeProperty(constants.S_IFREG);
};
Which shows that the information is contained within the mode property of the fs.Stats data structure.
I copied the code from kraken. I don't understand why there is a space between get and app(). Can someone please explain what's going on here?
var kraken = {
get app() {
return this._app;
},
use: function (route, delegate) {
//.....
}
}
No, in javascript a function cannot contain spaces. The code you are showing is using the get keyword to bind a property to a object.
get
Binds an object property to a function that will be called when that property is looked up.
Have a look to getters and setters in javascript.
It's a getter.
Check out this link.
The function is get and it's exposing a property called app.
For arrays I know you can do something like this:
function() {
}.observes("array.#each")
What I did was convert the object into an array and observe the properties with a #each, but is there a better way to observe object all property changes without converting it into an array?
You can observe isDirty to see if any of the object's values have been modified since last save (if you are using Ember Data).
Alternatively you can pass a comma separated list of properties to observes. This might be long if you have a lot of properties on your object, but will work.
A third approach could be to override setUnknownProperty() and set a property, a 'dirty flag' (or perform any action you may want in there.
There's also an old SO post that gives the following answer:
App.WatchedObject = Ember.Object.extend({
firstProp: null,
secondProp: "bar",
init: function(){
this._super();
var self = this;
Ember.keys(this).forEach(function(key){
if(Ember.typeOf(self.get(key)) !== 'function'){
self.addObserver(key, function(){
console.log(self.get(key));
});
}
});
}
});
You could probably split this out into a Mixin to keep your code DRY.
probably you could create something like a blabbermouth mixin and override the set method to get notified of property changes:
App.BlabbermouthMixin = Ember.Mixin.create({
set: function(keyName, value) {
this.set('updatedProperty', keyName);
this._super(keyName, value);
}
});
and observe the updatedProperty property?
You can get a list of properties in an object and apply them to a new property:
attrs = Ember.keys(observedObject);
var c = Ember.computed(function() {
// Do stuff when something changes
})
Ember.defineProperty(target, propertyName, c.property.apply(c, attrs));
Here is a working jsbin. Creating an observer instead of a property should be possible using a similar approach.
If I create an object property via Object.defineProperty() with a getter/setter method (an accessor descriptor) like:
var myObj = function myObj() {
var myFoo = 'bar';
Object.defineProperty(this, 'foo', {
enumerable: true,
get: function() {
return myFoo;
},
set: function(newValue) {
myFoo = newValue;
}
});
return this;
};
If I do something like var f = new myObj(); console.log(f) in Node, the output is something like:
{ foo: [Getter/Setter] }
console.log(f.foo) gets the proper 'bar' value, but is there a way to indicate that upon logging/inspecting, it should just run the getter and show the value?
First, it's important to understand why this happens. The logging functions don't run getters by design because your getter function could have side effects, whereas the logging function can guarantee that getting the value of a primitive doesn't.
When you pass an object to console.log, it's really just passing it off to the util module's inspect to format into human-readable text. If we look there, we see that the very first thing it does is check the property descriptor, and if the property has a getter, it doesn't run it. We can also see that this behavior is unconditional – there's no option to turn it off.
So to force getters to run, you have two options.
The simplest is to convert your object to a string before handing it off to console.log. Just call JSON.stringify(obj, null, 4), which will produce reasonably human-readable output (but not nearly as nice as util.inspect's). However, you have to take care to ensure that your object doesn't have any circular references and doesn't do something undesired in a toJSON function.
The other option is to implement a inspect function on your object. If util.inspect sees a function called inspect on an object, it will run that function and use its output. Since the output is entirely up to you, it's a much more involved to produce output that looks like what you'd normally get.
I'd probably start by borrowing code from util and stripping out the part about checking for getters.
This behavior is certainly intentional. I know I wouldn't want all the getter functions on an object running whenever I logged that object; that sounds like potential a debugging landmine, where debugging could alter the state of my program.
However, if indeed that is the behavior you want, you can add a new function:
Object.getPrototypeOf(console).logWithGetters = function(obj) {
var output = {};
var propNames = Object.getOwnPropertyNames(obj);
for(var i=0; i<propNames.length; ++i) {
var name = propNames[i];
var prop = Object.getOwnPropertyDescriptor(obj, name);
if(prop.get) {
output[name] = prop.get();
} else {
output[name] = obj[name];
}
}
// set output proto to input proto; does not work in some IE
// this is not necessary, but may sometimes be helpful
output.__proto__ = obj.__proto__;
return output;
}
This allows you to do console.logWithGetters(f) and get the output you want. It searches through an object's properties for getters (checking for the existence of Object.getOwnPropertyDescriptor(obj, propName).get) and runs them. The output for each property is stored in a new object, which is logged.
Note that this is a bit of a hacky implementation, as it doesn't climb the object's prototype chain.
I'm working with Dust.js and Node/Express. Dust.js documents the context helpers functions, where the helper is embedded in the model data as a function. I am adding such a function in my JSON data model at the server, but the JSON response to the browser doesn't have the function property (i.e. from the below model, prop1 and prop2 are returned but the helper property is not.
/* JSON data */
model: {
prop1: "somestring",
prop2: "someotherstring",
helper: function (chunk, context, bodies) {
/* I help, then return a chunk */
}
/* more JSON data */
I see that JSON.stringify (called from response.json()) is removing the function property. Not sure I can avoid using JSON.stringify so will need an alternative method of sharing this helper function between server/client. There probably is a way to add the helper functions to the dust base on both server and client. That's what I'm looking for. Since the Dust docs are sparse, this is not documented. Also, I can't find any code snippets that demonstrate this.
Thanks for any help.
send your helpers in a separate file - define them in a base context in dust like so:
base = dust.makeBase({foo:function(){ code goes here }})
then everytime you call your templates, do something like this:
dust.render("index", base.push({baz: "bar"}), function(err, out) {
console.log(out);
});
what this basically does is it merges your template's context into base, which is like the 'global' context. don't worry too much about mucking up base if you push too much - everytime you push, base recreates a new context with the context you supplied AND the global context - the helpers and whatever variables you defined when you called makeBase.
hope this helps
If you want stringify to preserve functions you can use the following code.
JSON.stringify(model, function (key, value) {
if (typeof(value) === 'function') {
return value.toString();
} else {
return value;
}
});
This probably doesn't do what you want though. You most likely need to redefine the function on the client or use a technology like nowjs.