Class constructor initializes and create objects/functions in a class. If I'm using functions, how would I initialize a function within the function?
This is the simple class
export default class MainProcess{
constructor() {
this.isReady = false
this.init()
}
init() {
this.setupApplicationMenu()
this.initWindowManager()
this.getIcons()
}
}
how can I initiate a MainPRocess Function?
While I'm not entirely sure I understand the question, I think you're asking "How can I create a function in a way that's similar to how I'm used to writing classes, but without using the class keyword?" Here's an example of that:
function Example () {
this.value = 10;
// instance method
this.print = function () {
console.log(this.value);
}
}
// static method
Example.printHello = function () {
console.log('hello world');
}
const example1 = new Example();
example1.print(); // 10
example1.value = 20;
example1.print(); //20
console.log(Object.getPrototypeOf(example1).constructor.name); // "Example"
const example2 = new Example();
example2. print(); //10
Example.printHello(); // "hello world"
Functions are part of the class. Classes are a grouping of functions(methods) and data(as properties). These functions are used to modify properties.
In the above example, you created a class MainProcess with some functions. However, functions defined in the init method is not present. The compiler will throw an error.
constructor is a special method used to create an object with that class.
If I'm using functions, how would I initialize a function within the
function?
It seems you are mixing two concepts function constructors in JS and Classes which are introduced later. Class is nothing, but a syntactic sugar on function constructor. JS is a prototype-based language.
difference b/w function and function constructor?
Functions created with the Function constructor do not create closures to their creation contexts; they always are created in the global scope. When running them, they will only be able to access their own local variables and global ones, not the ones from the scope in which the Function constructor was created. This is different from using Global_Objects/eval with code for a function expression.
var x = 10;
function createFunction1() {
var x = 20;
return new Function('return x;'); // this |x| refers global |x|
}
function createFunction2() {
var x = 20;
function f() {
return x; // this |x| refers local |x| above
}
return f;
}
var f1 = createFunction1();
console.log(f1()); // 10
var f2 = createFunction2();
console.log(f2()); // 20
I highly recommend you first understand the how JS has implemented class in it.
I have a function that I need to pass to a class I have defined in nodeJs.
The use case scenario is I want to give the implementer of the class the control of what to do with the data received from createCall function. I don't mind if the method becomes a member function of the class. Any help would be appreciated.
//Function to pass. Defined by the person using the class in their project.
var someFunction = function(data){
console.log(data)
}
//And I have a class i.e. the library.
class A {
constructor(user, handler) {
this.user = user;
this.notificationHandler = handler;
}
createCall(){
var result = new Promise (function(resolve,reject) {
resolve(callApi());
});
//doesn't work. Keeps saying notificationHandler is not a function
result.then(function(resp) {
this.notificationHandler(resp);
}) ;
//I want to pass this resp back to the function I had passed in the
// constructor.
//How do I achieve this.
}
callApi(){ ...somecode... }
}
// The user creates an object of the class like this
var obj = new A("abc#gmail.com", someFunction);
obj.createCall(); // This call should execute the logic inside someFunction after the resp is received.
Arrow functions (if your Node version supports them) are convenient here:
class A {
constructor(user, handler) {
this.user = user;
this.notificationHandler = handler;
}
createCall() {
var result = new Promise(resolve => {
// we're fine here, `this` is the current A instance
resolve(this.callApi());
});
result.then(resp => {
this.notificationHandler(resp);
});
}
callApi() {
// Some code here...
}
}
Inside arrow functions, this refers to the context that defined such functions, in our case the current instance of A. The old school way (ECMA 5) would be:
createCall() {
// save current instance in a variable for further use
// inside callback functions
var self = this;
var result = new Promise(function(resolve) {
// here `this` is completely irrelevant;
// we need to use `self`
resolve(self.callApi());
});
result.then(function(resp) {
self.notificationHandler(resp);
});
}
Check here for details: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions#No_separate_this
i tried found answer in stackoverflow and can't find any answer about this
i just started learning NodeJS . and i got a question, is there any way how can i exports whole object with his functions or i can exports only functions of object?
thanks for advice!
when i try it i got error like this
TypeError: object is not a function
i got simple code like this :
animal.js
var Animal = {
name : null,
setName : function(name) {
this.name = name;
},
getName : function() {
console.log("name of animal is " + this.name);
}
}
exports.Animal = Animal;
and server.js
var animal = require('./animal');
var ani = new animal.Animal();
The error is because new expects a Function while Animal is a plain Object.
Though, with the Object, you could use Object.create() to create instances:
// ...
var ani = Object.create(animal.Animal);
Otherwise, you'll have to define Animal as a constructor Function:
function Animal() {
this.name = null;
// ...
}
exports.Animal = Animal;
Note: Depending on precisely what you want to accomplish, Functions are a type of Object and can hold additional properties.
function Animal(name) {
this.name = name || Animal.defaultName;
}
Animal.defaultName = null;
JavaScript allows functions to be treated as objects--if you first define a variable as a function, you can subsequently add properties to that function. How do you do the reverse, and add a function to an "object"?
This works:
var foo = function() { return 1; };
foo.baz = "qqqq";
At this point, foo() calls the function, and foo.baz has the value "qqqq".
However, if you do the property assignment part first, how do you subsequently assign a function to the variable?
var bar = { baz: "qqqq" };
What can I do now to arrange for bar.baz to have the value "qqqq" and bar() to call the function?
It's easy to be confused here, but you can't (easily or clearly or as far as I know) do what you want. Hopefully this will help clear things up.
First, every object in Javascript inherits from the Object object.
//these do the same thing
var foo = new Object();
var bar = {};
Second, functions ARE objects in Javascript. Specifically, they're a Function object. The Function object inherits from the Object object. Checkout the Function constructor
var foo = new Function();
var bar = function(){};
function baz(){};
Once you declare a variable to be an "Object" you can't (easily or clearly or as far as I know) convert it to a Function object. You'd need to declare a new Object of type Function (with the function constructor, assigning a variable an anonymous function etc.), and copy over any properties of methods from your old object.
Finally, anticipating a possible question, even once something is declared as a function, you can't (as far as I know) change the functionBody/source.
There doesn't appear to be a standard way to do it, but this works.
WHY however, is the question.
function functionize( obj , func )
{
out = func;
for( i in obj ){ out[i] = obj[i]; } ;
return out;
}
x = { a: 1, b: 2 };
x = functionize( x , function(){ return "hello world"; } );
x() ==> "hello world"
There is simply no other way to acheive this,
doing
x={}
x()
WILL return a "type error". because "x" is an "object" and you can't change it. its about as sensible as trying to do
x = 1
x[50] = 5
print x[50]
it won't work. 1 is an integer. integers don't have array methods. you can't make it.
Object types are functions and an object itself is a function instantiation.
alert([Array, Boolean, Date, Function, Number, Object, RegExp, String].join('\n\n'))
displays (in FireFox):
function Array() {
[native code]
}
function Boolean() {
[native code]
}
function Date() {
[native code]
}
function Function() {
[native code]
}
function Number() {
[native code]
}
function Object() {
[native code]
}
function RegExp() {
[native code]
}
function String() {
[native code]
}
In particular, note a Function object, function Function() { [native code] }, is defined as a recurrence relation (a recursive definition using itself).
Also, note that the answer 124402#124402 is incomplete regarding 1[50]=5. This DOES assign a property to a Number object and IS valid Javascript. Observe,
alert([
[].prop="a",
true.sna="fu",
(new Date()).tar="fu",
function(){}.fu="bar",
123[40]=4,
{}.forty=2,
/(?:)/.forty2="life",
"abc".def="ghi"
].join("\t"))
displays
a fu fu bar 4 2 life ghi
interpreting and executing correctly according to Javascript's "Rules of Engagement".
Of course there is always a wrinkle and manifest by =. An object is often "short-circuited" to its value instead of a full fledged entity when assigned to a variable. This is an issue with Boolean objects and boolean values.
Explicit object identification resolves this issue.
x=new Number(1); x[50]=5; alert(x[50]);
"Overloading" is quite a legitimate Javascript exercise and explicitly endorsed with mechanisms like prototyping though code obfuscation can be a hazard.
Final note:
alert( 123 . x = "not" );
alert( (123). x = "Yes!" ); /* ()'s elevate to full object status */
Use a temporary variable:
var xxx = function()...
then copy all the properties from the original object:
for (var p in bar) { xxx[p] = bar[p]; }
finally reassign the new function with the old properties to the original variable:
bar = xxx;
var A = function(foo) {
var B = function() {
return A.prototype.constructor.apply(B, arguments);
};
B.prototype = A.prototype;
return B;
};
NB: Post written in the style of how I solved the issue. I'm not 100% sure it is usable in the OP's case.
I found this post while looking for a way to convert objects created on the server and delivered to the client by JSON / ajax.
Which effectively left me in the same situation as the OP, an object that I wanted to be convert into a function so as to be able to create instances of it on the client.
In the end I came up with this, which is working (so far at least):
var parentObj = {}
parentObj.createFunc = function (model)
{
// allow it to be instantiated
parentObj[model._type] = function()
{
return (function (model)
{
// jQuery used to clone the model
var that = $.extend(true, null, model);
return that;
})(model);
}
}
Which can then be used like:
var data = { _type: "Example", foo: "bar" };
parentObject.createFunc(data);
var instance = new parentObject.Example();
In my case I actually wanted to have functions associated with the resulting object instances, and also be able to pass in parameters at the time of instantiating it.
So my code was:
var parentObj = {};
// base model contains client only stuff
parentObj.baseModel =
{
parameter1: null,
parameter2: null,
parameterN: null,
func1: function ()
{
return this.parameter2;
},
func2: function (inParams)
{
return this._variable2;
}
}
// create a troop type
parentObj.createModel = function (data)
{
var model = $.extend({}, parentObj.baseModel, data);
// allow it to be instantiated
parentObj[model._type] = function(parameter1, parameter2, parameterN)
{
return (function (model)
{
var that = $.extend(true, null, model);
that.parameter1 = parameter1;
that.parameter2 = parameter2;
that.parameterN = parameterN;
return that;
})(model);
}
}
And was called thus:
// models received from an AJAX call
var models = [
{ _type="Foo", _variable1: "FooVal", _variable2: "FooVal" },
{ _type="Bar", _variable1: "BarVal", _variable2: "BarVal" },
{ _type="FooBar", _variable1: "FooBarVal", _variable2: "FooBarVal" }
];
for(var i = 0; i < models.length; i++)
{
parentObj.createFunc(models[i]);
}
And then they can be used:
var test1 = new parentObj.Foo(1,2,3);
var test2 = new parentObj.Bar("a","b","c");
var test3 = new parentObj.FooBar("x","y","z");
// test1.parameter1 == 1
// test1._variable1 == "FooVal"
// test1.func1() == 2
// test2.parameter2 == "a"
// test2._variable2 == "BarVal"
// test2.func2() == "BarVal"
// etc
Here's easiest way to do this that I've found:
let bar = { baz: "qqqq" };
bar = Object.assign(() => console.log("do something"), bar)
This uses Object.assign to concisely make copies of all the the properties of bar onto a function.
Alternatively you could use some proxy magic.
JavaScript allows functions to be
treated as objects--you can add a
property to a function. How do you do
the reverse, and add a function to an
object?
You appear to be a bit confused. Functions, in JavaScript, are objects. And variables are variable. You wouldn't expect this to work:
var three = 3;
three = 4;
assert(three === 3);
...so why would you expect that assigning a function to your variable would somehow preserve its previous value? Perhaps some annotations will clarify things for you:
// assigns an anonymous function to the variable "foo"
var foo = function() { return 1; };
// assigns a string to the property "baz" on the object
// referenced by "foo" (which, in this case, happens to be a function)
foo.baz = "qqqq";
var bar = {
baz: "qqqq",
runFunc: function() {
return 1;
}
};
alert(bar.baz); // should produce qqqq
alert(bar.runFunc()); // should produce 1
I think you're looking for this.
can also be written like this:
function Bar() {
this.baz = "qqqq";
this.runFunc = function() {
return 1;
}
}
nBar = new Bar();
alert(nBar.baz); // should produce qqqq
alert(nBar.runFunc()); // should produce 1
I'm writing a little nodeJS based email server. I have a Request object, and in it there's one static variable that stores all the users and is defined like so:
Request.publicMemory = new Object();
Request.publicMemory.users = new Object();
Request.prototype.getPublicMemory = function() {
return (Request.publicMemory);
};
I store User objects in it:
function User(params) {
this.mails = new Array();
this.sent = new Array();
var details = new Object();
details.username = params.username;
details.password = params.password
return;
}
As you can see there's also a static function that returns it.
Now, I can add uesrs and that change is actually made, but when I change anything in Request.publicMemory.usesrs[someuser] the change is always local to the function, and does not take effect in other places. Here's an example of how I do it:
function addMail(request) {
var users = request.getPublicMemory().users;
var to = request.parameters['to'];
users[to].mails.push(mail);
}
I've never used a static variable in nodeJS before, and I'm quite new to it so this might be silly, but I still can't solve it. Any ideas?
Thanks!