Create method inside function - javascript

I am trying to create method inside a function. I can make this such a way:
function sample() {};
sample.show = function() { alert() };
And I'll see the alert calling sample.show();. But for the reason of code beautifying I want to move all method declarations inside functions. I tried that:
function sample() {
sample.show = function() { alert() };
}
But I get: TypeError: Object function sample() has no method 'show'
Another ways I tried:
function sample() {
this.show = function() { alert() };
}
function sample() {
sample.prototype.show = function() { alert() };
}
function sample() {
this.prototype.method = function show () { alert() };
}
But result was the same. I can't even find any information about creating methods inside functions. Can you point me a right way?
UPD: I want to have ability to call sample() function which also does some stuff. So there are no solution in answers yet.
function sample() {
this.show = function() { alert() };
console.log('you called "sample()"');
}
sample(); // ==> you called "sample()"

First attempt:
function sample() {
sample.show = function() { alert() };
}
This would only create a "static" method on the sample function and only after executing it
console.log(sample.show);
//would show undefined on the console
sample();
console.log(sample.show);
//would then show the method definition as it has now been
//defined as a property of "sample"
Second Attempt:
function sample() {
this.show = function() { alert() };
}
This will only work if you create a instance of sample
console.log(sample.show);
//will print undefined as there is no property "show" on sample
sample();
console.log(window.show);
//will print the function, but since sample was executed without a
//context, show is created as a property of the global object
//in this case "window"
var d = new sample();
console.log(d.show);
//will print the function as we now have a instance of sample which
//show was made a property of
console.log(sample.prototype.show);
//will show undefined as you are not actually creating the "show" method
//on the constructor sample's prototype
Now with the prototype version:
function sample() {
sample.prototype.show = function() { alert() };
}
With this after you will be able to access the "show" method either through the instance or from the prototype chain, but for the prototype chain call to work you have to at least make one instance before hand
console.log(sample.prototype.show);
//will print undefined as "show" has not been defined on the prototype yet
var d = new sample();
console.log(d.show);
console.log(sample.prototype.show);
//Both will now print the function because the method has been defined
However the last one:
function sample() {
this.prototype.method = function show () { alert() };
}
Will not work at all as you can not access the prototype directly from the instance you will get a undefined error once you try to create an instance.
For it to work you would have to go through the constructor chain to set the method
function sample() {
this.constructor.prototype.method = function show () { alert() };
//is the same as doing
sample.prototype.method = function show(){ alert() };
}
So overall for your "beautifying" to work you have to call sample first, either directly, for the first one, or by creating an instance for the others.

the code in the sample function will not be executed until sample is called. So you could get your example to work by doing this:
function sample() {
sample.show = function() { alert() };
}
sample()
sample.show()

You can try this:
function sample() {
this.show = function() { alert() };
}
var x = new sample();
x.show();

you need to make sample an object
var sample = {
this.show = function() { alert() };
}

Related

Calling a JavaScript function from a nested objects function fails

On the simple example below and on JSFiddle here - https://jsfiddle.net/jasondavis/dnLzytju/ you can see the issue I have.
I can see why it could happen but I am not sure how to fix it while keeping the same JS structure.
The issue is when I define a JavaScript objects prototype functions and I have a 2nd level nested object which has a function and in that function I call a function on the parent/root level it fails.
This function from the code below this.nestedObject.nested_object_function() tries to call the function this.normal_function() however it fails and says:
Uncaught TypeError: this.normal_function is not a function
at Object.nested_object_function (VM2493:79)
I assume the reason is that this is referencing this.nestedObject instead of the parent object.
If that is the case, then how can I call that function like I am trying to do from the nested object function and call a parent function?
I have also tried calling JsLibTest.normal_function() as a test from the this.nestedObject.nested_object_function() function but I get the same error.
var JsLibTest = (function (document) {
"use strict";
var JsLibTest = function (){
// run init() function on initiation of a new JsLibTest object
this.init();
};
/**
* JsLibTest prototype functions
*/
JsLibTest.prototype = {
init: function() {
// as expected this function runs fine
this.normal_function();
// nested level objects functions run fune from parent level object function
this.nestedObject.nested_object_function();
},
normal_function: function() {
console.log('this.normal_function() ran');
},
nestedObject: {
// calling a function on the parent object fails here when called from this nested object function
nested_object_function: function() {
this.normal_function();
console.log('this.nestedObject.nested_object_function() ran');
},
}
};
return JsLibTest;
})(document);
// run it
$(document).ready(function(){
var Sidebar2 = new JsLibTest();
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
Your assessment is correct. this will be set to the nested object instead of the parent object and that's why it says the function is undefined.
What you need is a way of referencing the parent. Objects don't normally carry any information needed to reference an object which references them. This makes sense when you consider the fact that many objects can reference the same object internally.
You can either store a reference to the parent object and reference that in the nested function:
var nested = {
g() {
this.parent.f();
}
};
var parent = {
f() {
console.log('called');
}
};
nested.parent = parent;
nested.g();
or you can use Function.prototype.call (or something similar) to set the correct context.
var obj = {
f() {
console.log('called');
},
g() {
this.nested.nested_f.call(this);
},
nested: {
nested_f() {
this.f();
}
}
};
obj.g();
Putting the last solution in to the context of your problem:
var JsLibTest = (function(document) {
"use strict";
var JsLibTest = function() {
this.init();
};
JsLibTest.prototype = {
init: function() {
this.normal_function();
// NOTICE: Using .call here to set the context
this.nestedObject.nested_object_function.call(this);
},
normal_function: function() {
console.log('this.normal_function() ran');
},
nestedObject: {
nested_object_function: function() {
this.normal_function();
console.log('this.nestedObject.nested_object_function() ran');
}
}
};
return JsLibTest;
})(document);
// run it
$(document).ready(function() {
var Sidebar2 = new JsLibTest();
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
You are correct that scope doesn't have access to the parent. Easy solution would be that you pass parent to the nested object like:
this.nestedObject.nested_object_function(this);
then in your nested function call parent as:
nested_object_function: function(self) {
self.normal_function();
alert('this.nestedObject.nested_object_function() ran');
}
since you pass this (parent) as self you can then call it from nested one.
At first, the Object must be unique for Each, having a prototype:
this.nestedObject=Object.create(this.nestedObject);
var JsLibTest = function (){
// run init() function on initiation of a new JsLibTest object
this.init();
//bind to childs:
this.nestedObject.parent=this;
};
Now you can use this.parent inside of your inner function...
this.parent.normal_function();
If you want this to be the parent, bind:
var JsLibTest = function (){
// run init() function on initiation of a new JsLibTest object
this.init();
//bind to childs:
for(i in this.nestedObject){
var el=this.nestedObject[i];
if(typeof el==="function"){
this.nestedObject[i]=el.bind(this);
}
}
};
To make it easier, may use sth like that ( a helper function):
getfunc:function(...a){
a.reduce((obj,key)=>obj[key],this).bind(this);
}
Use like this:
JsLibTestInstance("nestedObject","nestedobject_function")();
Yea, you are right that the this value in your JSLibTest.prototype.nestedObject function is pointing to nestedObject and not JSLibTest.
If you want to maintain the same call signature, you can declare nestedObject as an IIFE:
nestedObject: (function() {
var that = this;
return {
nested_object_function: function() {
console.log(that);
// this.normal_function();
alert('this.nestedObject.nested_object_function() ran');
}
}
}())
https://jsfiddle.net/dnLzytju/1/
Note: You probably do not want to declare your prototype that way is it effectively deletes all the native prototype methods of the object.
To author your code in a similar way, consider using Object.assign to help you out.
var foo = Object.assign({}, Function.prototype, {
bar() {
console.log("Hello!")
}
});
foo.bar();

How Come public method is not printing in a IIFE?

Shouldn't hello be printed in the console because of the return statement? The code is immediately invoked because of the () at the end so why isn't it printing?
var Module = (function () {
var privateMethod = function () {
// private
};
var someMethod = function () {
// public
console.log('hello');
};
var anotherMethod = function () {
// public
};
return {
someMethod: someMethod,
anotherMethod: anotherMethod
};
})();
return {
someMethod: someMethod, // just a function reference
anotherMethod: anotherMethod // again a function reference
};
So, you're not calling the function. You're just returning the function reference attached to a property of an object. Try to use comma operator here, which evaluates to the right most statement, whilst executing someMethod() function.
return {
someMethod: someMethod(), someMethod, // first getting called and someMethod ref is passed to the property
anotherMethod: anotherMethod
};
It's because of the var keyword on the top infront of Module.
f you do the following in the console:
var a = 5 // a is set to 5 yet undefined is shown in the console.
If you were to take off the var keyword:
a = 5 // a is again set to 5 yet 5 is shown in the console.
But in your real code you would want to use the var keyword.
So simply put it's just the console's way of outputting like that, idk why.
Enlighting more,
function itseld is object of Function (see https://msdn.microsoft.com/en-us/library/ie/x844tc74%28v=vs.94%29.aspx)
So Basically you are adding a reference to object of type Function, which is not IIFE.

javascript prototype how to create object

I'm currently learning prototyping in javascript, i wrote the below and it seems to work fine when i use it. my question was why do i need the () at the end of the prototype declaration, without that if i try to make an instance of the object I get an error.
var MyTest = function (agencyId, dataId) {
this.agencyId= agencyId;
this.dataId= dataId;
};
MyTest.prototype = function () {
var setObservables = function () {
...
},
init = function (url) {
...
};
// public members
return {
init: init
};
}();
to use it I call it like
var obj = new DetailsDivisionKO(1, 2);
obj.init(actionUrl);
this works fine, but I'm confused about the }(); at the end of the public members section, why is that needed and I can not have that and still use the above code to call it? As without that if i try to call the above code I get a error stating:
Uncaught TypeError: Object [object Object] has no method 'init'
What you have is an IIFE. Its an imidiately invoked function. You are basically creating a closure. You are exposing your init function while preserving a true private scope to your setObservables function. So every time you create a new instance of the constructor, your init function will always be in the prototype. But setObservables will not. In your example you could only access setObservables function internally (hence private scope). Usually you would do that if you only want your init function to call your private functions which in your case is setObservables. But if this is not what you want, you simply can do this:
var MyTest = function (agencyId, dataId) {
this.agencyId= agencyId;
this.dataId= dataId;
};
MyTest.prototype = {
setObservables: function () {
...
},
init: function (url) {
...
}
}
Now every time you will create a new instance of MyTest, both of your functions will be in its prototype.
var test = new MyTest(1, 2);
test.init();
test.setObservables();

Javascript methods use

I am trying to create a class in JavaScript that would be inherited and than some of its methods would be overridden.
I am using the following structure :
function MyClass()
{
this.myvar = null;
this.someotherVar = { someFunction: function(a,b){ function1(a,b); })
}
// some functions
MyClass.prototype.functionA = function() {..}
MyClass.prototype.functionB = function() {functionC();}
//some functions that would be overrided
MyClass.prototype.function1= function() {...}
MyClass.prototype.functionC= function() {...}
Now I have 2 problems:
Might functionC be a problem to use in functionB because it is defined afterwards?
How can I relate to function1 inside someFunction in the right way?
1. Might functionC be a problem to use in functionB because it is defined afterwards?
No. You just have to call it properly:
function() { this.functionC(); }
// ^^^^^
otherwise the function won't be found.
Of course you also have to make sure that functionB is only called once functionC is defined.
2. How can I relate to function1 inside someFunction in the right way?
A tiny problem is that someFunction is not a method of the instance but of another object. To still call the correct function1, you can store a reference to the instance in a variable:
function MyClass() {
var self = this;
this.myvar = null;
this.someotherVar = {
someFunction: function(a,b){
self.function1(a,b);
}
};
}

Javascript accessing functions of same class

In the following code:
function xyz(x) {
//something
this.x = x;
}
xyz.prototype = {
a: function () {
//do something
},
b: function () {
//pre
this.a();
//post
}
}
the call of this.a() gives the warning of method not supported. So I tried using xyz.prototype.a.call(this) instead. But it does not maintain the value of x. What do I do to call one method of a class from other?
Given your code, if you write:
var myXyz = new xyz("hello");
then calling
myXyz.b();
should correctly get to the "a()" function on the prototype. However, if you do something like this:
var otherB = myXyz.b;
otherB();
then it will not work, because there's no context object (that is, the this value inside "b()" won't be set correctly to an instance of "xyz"). That often happens when a function is being used as an event handler:
something.onclick = myXyz.b;
The event handler, when called, won't have an "xyz" instance to work with. Instead of that, therefore, you could write:
something.onclick = function() { myXyz.b(); };
which clearly ensures that there's an "xyz" object.

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