Private methods in javascript.

Question

How do I create private methods in javascript classes?

Answer 1

with an IIFE (immediatly invoked function execution):

var MyClass = (function() {
function private() {
alert('only code in this IIFE can access this private function');
alert('from private, this = '+JSON.stringify(this,null,' '));
}
return class MyClass {
constructor(props) {
Object.assign(this,props);
}
public() {
alert('public method');
private.call(this);
}
};
})();

that define a private function accessible only from code inside the IIFE where it is defined...

to use it as an object method, call it by binding 'this' to it (see Function methods bind, call, and/or apply)

https://medium.com/@jhawleypeters/javascript-call-vs-apply-vs-bind-61447bc5e989

https://www.codementor.io/@niladrisekhardutta/how-to-call-apply-and-bind-in-javascript-8i1jca6jp

Answer 2

Simple google search lead me to https://stackoverflow.com/questions/22156326/private-properties-in-javascript-es6-classes
I hop it helps

Answer 3

You could use closure to set private fields and methods. Here an example

var calnums = function() {
// private method
var getprivatenum = function () {
// secret business logic here to get 100 ...
return 100;
}

// privte field
var num = getprivatenum(); // init num

return {
// public method
add: function(n) { // add input with private num
num += n;
},

// public method
sum: function() { // return private num
return num;
}
}
}

try {
var inputnums = calnums();

inputnums.add(2); // add with privatenum
inputnums.add(3);
inputnums.add(6);
inputnums.add(4);
inputnums.add(5);
var sum = inputnums.sum();
console.log(sum); // get 120

var inputnums1 = calnums();
inputnums1.getprivatenum();
} catch (err) {
// error: can't access private method
console.log(err.message);
}

https://code.sololearn.com/chN993zel4NN/?ref=app

Answer 4

I only noticed that OP mentions private method in class now.

Class properties are public by default and can be examined or modified outside the class. There is however a stage 3 proposal to allow defining private class fields using a hash # prefix.

More information
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes/Private_class_fields

I tried to convert my previous example to class here, please check it out.

class CallNum {
// privte field
#num = 0; // init num

constructor() {
// console.log("init");
this.#num = this.#getPrivateNum()
}

// private method
#getPrivateNum() {
// secret business logic here to get 100 ...
return 100;
}

// public method
add(n) { // add input with private num
this.#num += n;
}

// public method
sum() { // return private num
return this.#num;
}
}

full code: (webview and 74)
https://code.sololearn.com/We9U8jxXR40H/?ref=app

Answer 5

Mirielle[ Exams ]
you're right about strictly private methods: they are still mostly not supported...

however, under the hood, private methods (when supported) are only a way of binding a function with 'this', by hidding the bind/call/apply stuff ^^