This question already has answers here:
How do I make JavaScript Object using a variable String to define the class name?
(10 answers)
Create object from class name in JavasScript ECMAScript 6
(8 answers)
Closed 4 years ago.
I have a question which shouldn't be to difficult, but I've been spending days and can't seem to find the answer. All the solutions I found didn't help me, they all threw errors.
I made a Class in Javascript and want to create a new instance dynamically, so that I can instantiate multiple classes depending on the parameter in a function. It doesn't seem te work, and I wonder why.
settings.js and main.js are loaded via <script> tag in the HTML file, with settings.js being loaded first.
main.js
let myClass = new settings(); // Works
let myClass2 = test('settings'); // Error: Uncaught TypeError: param is not a constructor
function test(param){
return new param();
}
settings.js
class settings{
constructor(){
console.log("works");
}
}
Thanks for any help!
Related
This question already has answers here:
js dynamically access private fields (properties/members)
(5 answers)
Can I set a private class field using a variable as identifier? How?
(1 answer)
How to get access to private field via square brackets in JavaScript
(2 answers)
Closed last year.
It's acknowledge that we can access a property of an object by two ways :foo.bar and foo['bar'], but when I use the new feature # to declare a private member in class, it won't work properly:
class FooBar{
constructor(){}
testCall(name){
this[name]()
}
bar(){console.log(1)}
#bar(){console.log(2)}
}
let foo = new FooBar();
foo.testCall('bar'); //this line works properly
foo.testCall('#bar'); //Uncaught TypeError: this[name] is not a function
Can someone please tell how can I modify it to make the code work properly
This question already has answers here:
What is the difference between const and const {} in JavaScript
(4 answers)
Closed 4 years ago.
So while I was making my react native app, I tried to use an API from
https://github.com/uport-project/react-native-uport-connect and there is a syntax that I've yet to understand.
May I know what does const { uport, MNID } mean from this code
import configureUportConnect from 'react-native-uport-connect'
const { uport, MNID } = configureUportConnect({
appName: 'uPort Demo',
appAddress: '2oeXufHGDpU51bfKBsZDdu7Je9weJ3r7sVG',
privateKey:'<PRIVATE_KEY>',
})
Im quite new to this and this code is placed on a seperate js file and im trying to export const { uport, MNID } so I could use it in my Components and im not sure if it's a variable, object or some js syntax. Thank you!
This is called destructuring, and it means you are assigning your variables, not to the object that the function returns, but to the individual properties of that object, specifically the properties at the keys uport and MNID. The alternative syntax would be to say const variableName = // etc... and then you would access the properties like: variableName.uport.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment#Object_destructuring
This question already has answers here:
How do I make JavaScript Object using a variable String to define the class name?
(10 answers)
Get global variable dynamically by name string in JavaScript
(6 answers)
Closed 5 years ago.
JS6, Browser
How to create the instance of the class by its string name? For example I have a string Foo and I need to create an instance of Foo class. I don't want to write such construction:
let className = getClassName(); // returns 'Foo', `Stuff` or other
...
let item = null;
if(`Foo` == className){
item = new Foo();
}
else if(`Stuff` == className){
item = new Stuff();
}
UPD
I try to get access to my class constructor through the window object but I have the problem: it returns undefined. But my class exists and browser knows it:
What you are trying to do is what you should do, in my opinion. This is a standard way of instantiating objects when the type of object is known at runtime, and is called the Factory Method Pattern.
You should avoid duplicating this everywhere in your code by using a factory object that will encapsulate the object creation. This factory object will have a method that will take the type name as its parameter.
Please use google: Instantiate a JavaScript Object Using a String to Define the Class Name
var myObject = window[classNameString];
P.S. I copy pasted your title of question and added javascript in front.
This question already has answers here:
Create an instance of a class in ES6 with a dynamic name? [duplicate]
(2 answers)
Closed 7 years ago.
I have a use case where I need to persist the name of a given class in a cookie so that I can create an instance of it later when the client returns. I would like to be able to do something like this:
class MyClass {
}
var a1 = new MyClass()
var className = a.class.name()//like in Java..
var a2 = Class.forName(className).newInstance();
Is this possible in ES6? Specifically I am looking for some way to get the name fo the class as a string,
You should be able to get the name of the class by calling a1.constructor.name1
Since classes are really fancy syntax for functions, if the class exists on the window object you could probably then do something like var a2 = new window[className](); but that really depends what scope you are working in.
This question already has answers here:
Constructors in JavaScript objects
(19 answers)
Closed 8 years ago.
my English is not so good, but i try to explain my self clear.
I just started learn JS objects and stumbled upon the problem that i can't understand.
I got a simple object like
var cars = {
doors: 4,
wheels: 4
}
and when i trying to create an object like this:
var Opel = new car()
I got an error Uncaught TypeError: object is not a function
And when i do it like this :
Opel = Object.create(cars)
all going fine.
And when i writing a an Object like this :
function cars() {}
a method to declare the object with new, work correctly.
I can't understand what the difference between thous two type of writing the objects.
Thanks for advice.
You didn't understand prototyping correct.
To define a class you create a simple function, like:
function Car(){
this.doors = 4; //For instance, not really necessary
}
You can set properties on this in the function.
Then you define a prototype, every object of class "Car" will have all this properties (and "methods"):
Car.prototype = {
doors: 4, //we don't need to set this again if we already did in the constructor, but I'll leave if it anyway
wheels: 4
}
Please see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Introduction_to_Object-Oriented_JavaScript for more.