I created a class with a method:

class MyClass{

myMethod(){
    return ...;
}}

After that I push every instance of that class to an array:

let myList = [];
myList.push(myClass)

How can I call myMethod() within a loop? This code fails:

for (var i = 0; myList.length; i++) {
    myList[i].myMethod();
}

Uncaught TypeError: Cannot read property 'myMethod' of undefined

Thx, piccus

I created a class with a method:

class MyClass{

myMethod(){
    return ...;
}}

After that I push every instance of that class to an array:

let myList = [];
myList.push(myClass)

How can I call myMethod() within a loop? This code fails:

for (var i = 0; myList.length; i++) {
    myList[i].myMethod();
}

Uncaught TypeError: Cannot read property 'myMethod' of undefined

Thx, piccus

• javascript
• loops
• object
• for-loop

Share Improve this question Follow asked May 24, 2017 at 6:04 piccuspiccus 17122 silver badges99 bronze badges 0

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2 Answers 2

Sorted by: Reset to default 2

You should crate an instance with new operator in order to call a method:

class myClass{
  myMethod(){
    console.log('hi');
  }
}

let myList = [];
myList.push(new myClass())
myList.push(new myClass())
myList.push(new myClass())
myList.push(new myClass())
myList.push(new myClass())

for (var i = 0; i < myList.length; i++) {
    myList[i].myMethod();
}

If you need to call this method without instance, define it as static:

class myClass{
  static myMethod(){ // notice static
    console.log('hi');
  }
}

let myList = [];
myList.push(myClass)
myList.push(myClass)
myList.push(myClass)
myList.push(myClass)
myList.push(myClass)

for (var i = 0; i < myList.length; i++) {
    myList[i].myMethod();
}

You could keep track of each instance of MyClass by pushing this into myList when the constructor is called. That way you don't have to keep remembering to push into myList each time you construct a new MyClass instance.

var myList = [];

function MyClass (theAnswer) {
  this.theAnswer = theAnswer;  
  this.getTheAnswer = function () {
    console.log(this.theAnswer);
  };
  
  // Keep track of all instances of MyClass here.
  myList.push(this);
}

new MyClass(42);
new MyClass(null);
new MyClass('Dunno');

for (var i = 0; i < myList.length; i++) {
    myList[i].getTheAnswer();
}