I'm wondering what the difference, or if any, the following JS is for building up an object. Is it a style thing/standards thing? If so, which is most common?
Example 1:
var MyNamspace = {
options: { test: 10 },
someFunction: function() { alert("Hello"); }
}
Example 2:
var MyNamespace = {};
MyNamespace.options = { test: 10 };
MyNamespace.someFunction = function() { alert("Hello"); }
Thanks.
There is no significant difference between the two (although the second is probably marginally slower).
The first example is more usual.
The first MyNamspace is missing an "e", else there is no functional difference.
The second pattern is used when there is already an object with properties (like someFunc.prototype) which you want to extend, but you'd need to leave the overwriting part (MyNamespace = {};) away.
The second option modifies an existing type, so while equal, the second is modifying the signature of an existing type, just like you could do: MyClass.prototype.someFunction = function() { }
This is where JavaScript can be conveniently flexible.
Related
I'd like to 'proxy' (not sure if that's the term at all) a function inside a function object for easy calling.
Given the following code
function Soldier() {
this.el = $("<div></div>").addClass('soldier');
this.pos = this.el.position; // $(".soldier").position(), or so I thought
}
In the console:
s = new Soldier();
$("#gamemap").append(s.el); // Add the soldier to the game field
s.pos === s.el.position // this returns true
s.el.position() // Returns Object {top: 0, left: 0}
s.pos() // Returns 'undefined'
What am I doing wrong in this scenario and is there an easy way to achieve my goal (s.pos() to return the result of s.el.position()) ?
I thought about s.pos = function() { return s.el.position(); } but looks a bit ugly and not apropriate. Also I'd like to add more similar functions and the library will become quite big to even load.
When you're calling s.pos(), its this context is lost.
You can simulate this behavior using call():
s.pos.call(s); // same as s.pos()
s.pos.call(s.el); // same as s.el.position()
This code is actually ok:
s.pos = function() { return s.el.position(); }
An alternative is using bind():
s.pos = s.el.position.bind(el);
You can use the prototype, that way the functions will not be created separately for every object:
Soldier.prototype.pos = function(){ return this.el.position(); }
I'd recommend to use the prototype:
Soldier.prototype.pos = function() { return this.el.position(); };
Not ugly at all, and quite performant actually.
If you want to directly assign it in the constructor, you'll need to notice that the this context of a s.pos() invocation would be wrong. You therefore would need to bind it:
…
this.pos = this.el.position.bind(this.el);
It's because the context of execution for position method has changed. If you bind the method to work inside the element context it will work.
JS Fiddle
function Soldier() {
this.el = $("<div></div>").addClass('soldier');
this.pos = this.el.position.bind(this.el);
}
var s = new Soldier();
$("#gamemap").append(s.el);
console.log(s.pos());
I am creating a form and I am trying to find a simple, elegant way of handling to see if all inputs exist.
Form = Ember.Object.extend({
// section 1
name: null,
age: null,
isABoolean: null,
// section 2
job: null,
numberOfSiblings: null,
isComplete: Ember.computed.and('_isSection1Complete', '_isSection2Complete'),
_isSection1Complete: function() {
var isPresent = Ember.isPresent;
return isPresent(this.get('name')) && isPresent(this.get('age')) && isPresent(this.get('isABoolean'));
}.property('name', 'age', 'isABoolean'),
_isSection2Complete: function() {
var isPresent = Ember.isPresent;
return isPresent(this.get('job')) && isPresent(this.get('numberOfSiblings'));
}.property('job', 'numberOfSiblings')
});
However, this doesn't seem to scale. My actual application will have many sections (over 20 sections).
I am looking into trying to create a re-usable computed property that fits my needs. Take for example the code of what I am going for:
Form = Ember.Object.extend({
// properties...
isComplete: Ember.computed.and('_isSection1Complete', '_isSection2Complete'),
_isSection1Complete: Ember.computed.allPresent('name', 'age', 'isABoolean'),
_isSection2Complete: Ember.computed.allPresent('job', 'numberOfSiblings')
});
I feel that this is a common case, but I'm failing to find the correct computed properties on how to execute this, so I would like to make my own.
Two questions:
Where's the best place to define the custom computed property? Can I just attach a function to Ember.computed?
Is there an easier way to solve this? I feel like I'm overlooking something simple.
As for Question #1,
You can define a custom computed helper in the App namespace. In this example, I created a new computed helper called allPresent that checks each property passed in against Ember.isPresent.
App.computed = {
allPresent: function (propertyNames) {
// copy the array
var computedArgs = propertyNames.slice(0);
computedArgs.push(function () {
return propertyNames.map(function (propertyName) {
// get the value for each property name
return this.get(propertyName);
}, this).every(Ember.isPresent);
});
return Ember.computed.apply(Ember.computed, computedArgs);
}
};
It can be used like this, per your example code:
_isSection2Complete: App.computed.allPresent(['job', 'numberOfSiblings'])
I adapted this from the approach here: http://robots.thoughtbot.com/custom-ember-computed-properties
As for Question #2, I can't think of a simpler solution.
I had to make a minor adjustment to Evan's solution, but this works perfectly for anyone else that needs it:
App.computed = {
allPresent: function () {
var propertyNames = Array.prototype.slice.call(arguments, 0);
var computedArgs = propertyNames.slice(0); // copy the array
computedArgs.push(function () {
return propertyNames.map(function (propertyName) {
// get the value for each property name
return this.get(propertyName);
}, this).every(Ember.isPresent);
});
return Ember.computed.apply(Ember.computed, computedArgs);
}
};
This can now be used as such:
_isSection2Complete: App.computed.allPresent('job', 'numberOfSiblings')
I'm trying to learn javascript. As part of that effort, I am writing a basic minimax AI. I have the following methods:
Computer.prototype.expand = function(node) {
/* adds all state action pairs to the node.successors array */
};
Computer.prototype.getMove = function(boardAr) {
console.log("getMove");
var b2 = boardAr.slice();
var i;
var action;
this.root = new TNode(b2, this.mark);
this.root.AIPlayedLast = false;
this.expand(this.root);
this.root.successors.forEach(this.minVal);
action = maxNode(root.successors);
this.draw(action);
registerMove(action, this.mark);
};
Computer.prototype.minVal = function(node) {
if (node.isTerminal) {
return;
} else {
this.expand(node);
node.successors.forEach(maxVal);
node.utility = this.minNode(node.successors).utility;
}
};
When the getMove method is called the subsequent call to expand goes as expected. But, when expand is called from the minVal method I get: Uncaught TypeError: undefined is not a function. I'm utterly perplexed by this. Any help/suggestions would be greatly appreciated.
I think the reason is in this row:
this.root.successors.forEach(this.minVal);
You pass minVal as contextless reference, it will not be called in a context of your Computer instance (this)
Here is how you can improve it:
var self = this;
this.root.successors.forEach(function() {
self.minVal.apply(self,arguments);
})
The simplest and quickest solution is just to change
this.root.successors.forEach(this.minVal);
to
this.root.successors.forEach(this.minVal.bind(this))
This solves the problem in the same as the other answers, but in a way some might consider more compact.
Or, you can pass a "this" to the forEach function as the second argument, a somewhat under-utilized feature of forEach:
this.root.successors.forEach(this.minVal, this)
This feature is also available on other Array prototype methods that take functions, including map, filter, some, every (but not reduce and reduceRight).
ES6 arrow functions handle this differently, so you can do
this.root.successors(forEach(e => this.minVal(e)));
The forEach() method might be called for each of the successors. So, you pass the Computer::minVal method (this.minVal), but with the TNode(?) as this-pointer. Try:
var that = this;
this.root.successors.forEach(function(node) {
that.minVal(node));
});
I've a page that is generated dynamically, and that includes certain number (user-dynamically-defined) of advanced scatter plot charts. I intend to create a JavaScript object which defines the scatter plot itself, i.e. which takes some parameters, some data, and some container ID, and which will create the various elements needed to obtain the visualisation: canvas elements, toolbar, etc.. To do so, I started with the following (simplified) class:
(function () {
if (!this.namespace) { this.namespace = {};}
this._instances = { index: 0 };
this.namespace.ScatterPlot = function (containerId, file, options) {
_instances.index ++;
this.id = this.containerId+"-"+_instances.index ;
this.containerId = containerId ;
_instances [this.id] = this;
// ... Do stuffs with file and options ...
// Initialize elements once the DOM is ready
$(this.updateDOM);
}
namespace.ScatterPlot.prototype = {
updateDOM: function() {
$("<canvas>")
.click(clickCallback)
.appendTo("#"+this.containerId);
//(...)
},
clickCallback: function() {
alert("Some click: "+this.id);
}
}
})();
Each object can be created with:
var v1 = new namespace.ScatterPlot("container1", "foo", "foo");
var v2 = new namespace.ScatterPlot("container2", "foo", "foo");
There are two problems here: (1) in updateDOM, 'this' does not make reference to my initial ScatterPlot object, which means that this example will never work, and (2) similarly, the clickCallback will not be able reference the scatterplot with 'this' either.
I'm new to javascript, and I'm still struggeling to understand the logic of OO programming in javascript, so the question is: I'm I taking the wrong direction here ? After some digging, I could roughly achieve what I wanted by passing this to updateDOM:
$(this.updateDOM(this)); // This blows my eyes but does the trick, at least partially
updateDOM: function(that) {
$("<canvas>")
.click(that.clickCallback)
.appendTo("#"+that.containerId);
//(...)
},
clickCallback: function() {
// Not working either... Should pass 'that' to the function too
alert("Some click: "+this.id);
}
But I don't feel this patters to be very elegant... And the problem is not fixed either regarding the click callback.
Thoughts ?
Have a look at MDN's introduction to the this keyword.
The standard ways of dealing with that issue are using a that variable - not as an argument, but in a separate function:
var that = this;
$(function() {
that.updateDOM();
});
// or
$(this.getClickCallback());
...
namespace.ScatterPlot.prototype.getClickCallback = function() {
var that = this;
return function clickCallback(e) {
alert("Some click: "+that.id);
};
};
Alternatively, you can always use .bind() (or $.proxy for older browsers) which do quite what the second example does in a more generic way:
$(this.clickCallback.bind(this));
I have a function, a(), that I want to override, but also have the original a() be performed in an order depending on the context. For example, sometimes when I'm generating a page I'll want to override like this:
function a() {
new_code();
original_a();
}
and sometimes like this:
function a() {
original_a();
other_new_code();
}
How do I get that original_a() from within the over-riding a()? Is it even possible?
Please don't suggest alternatives to over-riding in this way, I know of many. I'm asking about this way specifically.
You could do something like this:
var a = (function() {
var original_a = a;
if (condition) {
return function() {
new_code();
original_a();
}
} else {
return function() {
original_a();
other_new_code();
}
}
})();
Declaring original_a inside an anonymous function keeps it from cluttering the global namespace, but it's available in the inner functions.
Like Nerdmaster mentioned in the comments, be sure to include the () at the end. You want to call the outer function and store the result (one of the two inner functions) in a, not store the outer function itself in a.
The Proxy pattern might help you:
(function() {
// log all calls to setArray
var proxied = jQuery.fn.setArray;
jQuery.fn.setArray = function() {
console.log( this, arguments );
return proxied.apply( this, arguments );
};
})();
The above wraps its code in a function to hide the "proxied"-variable. It saves jQuery's setArray-method in a closure and overwrites it. The proxy then logs all calls to the method and delegates the call to the original. Using apply(this, arguments) guarantees that the caller won't be able to notice the difference between the original and the proxied method.
Thanks guys the proxy pattern really helped.....Actually I wanted to call a global function foo..
In certain pages i need do to some checks. So I did the following.
//Saving the original func
var org_foo = window.foo;
//Assigning proxy fucnc
window.foo = function(args){
//Performing checks
if(checkCondition(args)){
//Calling original funcs
org_foo(args);
}
};
Thnx this really helped me out
You can override a function using a construct like:
function override(f, g) {
return function() {
return g(f);
};
}
For example:
a = override(a, function(original_a) {
if (condition) { new_code(); original_a(); }
else { original_a(); other_new_code(); }
});
Edit: Fixed a typo.
Passing arbitrary arguments:
a = override(a, function(original_a) {
if (condition) { new_code(); original_a.apply(this, arguments) ; }
else { original_a.apply(this, arguments); other_new_code(); }
});
The answer that #Matthew Crumley provides is making use of the immediately invoked function expressions, to close the older 'a' function into the execution context of the returned function. I think this was the best answer, but personally, I would prefer passing the function 'a' as an argument to IIFE. I think it is more understandable.
var a = (function(original_a) {
if (condition) {
return function() {
new_code();
original_a();
}
} else {
return function() {
original_a();
other_new_code();
}
}
})(a);
The examples above don't correctly apply this or pass arguments correctly to the function override. Underscore _.wrap() wraps existing functions, applies this and passes arguments correctly. See: http://underscorejs.org/#wrap
In my opinion the top answers are not readable/maintainable, and the other answers do not properly bind context. Here's a readable solution using ES6 syntax to solve both these problems.
const orginial = someObject.foo;
someObject.foo = function() {
if (condition) orginial.bind(this)(...arguments);
};
I had some code written by someone else and wanted to add a line to a function which i could not find in the code. So as a workaround I wanted to override it.
None of the solutions worked for me though.
Here is what worked in my case:
if (typeof originalFunction === "undefined") {
originalFunction = targetFunction;
targetFunction = function(x, y) {
//Your code
originalFunction(a, b);
//Your Code
};
}
I've created a small helper for a similar scenario because I often needed to override functions from several libraries. This helper accepts a "namespace" (the function container), the function name, and the overriding function. It will replace the original function in the referred namespace with the new one.
The new function accepts the original function as the first argument, and the original functions arguments as the rest. It will preserve the context everytime. It supports void and non-void functions as well.
function overrideFunction(namespace, baseFuncName, func) {
var originalFn = namespace[baseFuncName];
namespace[baseFuncName] = function () {
return func.apply(this, [originalFn.bind(this)].concat(Array.prototype.slice.call(arguments, 0)));
};
}
Usage for example with Bootstrap:
overrideFunction($.fn.popover.Constructor.prototype, 'leave', function(baseFn, obj) {
// ... do stuff before base call
baseFn(obj);
// ... do stuff after base call
});
I didn't create any performance tests though. It can possibly add some unwanted overhead which can or cannot be a big deal, depending on scenarios.
So my answer ended up being a solution that allows me to use the _this variable pointing to the original object.
I create a new instance of a "Square" however I hated the way the "Square" generated it's size. I thought it should follow my specific needs. However in order to do so I needed the square to have an updated "GetSize" function with the internals of that function calling other functions already existing in the square such as this.height, this.GetVolume(). But in order to do so I needed to do this without any crazy hacks. So here is my solution.
Some other Object initializer or helper function.
this.viewer = new Autodesk.Viewing.Private.GuiViewer3D(
this.viewerContainer)
var viewer = this.viewer;
viewer.updateToolbarButtons = this.updateToolbarButtons(viewer);
Function in the other object.
updateToolbarButtons = function(viewer) {
var _viewer = viewer;
return function(width, height){
blah blah black sheep I can refer to this.anything();
}
};
Not sure if it'll work in all circumstances, but in our case, we were trying to override the describe function in Jest so that we can parse the name and skip the whole describe block if it met some criteria.
Here's what worked for us:
function describe( name, callback ) {
if ( name.includes( "skip" ) )
return this.describe.skip( name, callback );
else
return this.describe( name, callback );
}
Two things that are critical here:
We don't use an arrow function () =>.
Arrow functions change the reference to this and we need that to be the file's this.
The use of this.describe and this.describe.skip instead of just describe and describe.skip.
Again, not sure it's of value to anybody but we originally tried to get away with Matthew Crumley's excellent answer but needed to make our method a function and accept params in order to parse them in the conditional.