Javascript - TypeError: Object [object Object] has no method 'forEach'

Question

I am writing a telemetry function in my code. I am using the Performance.getEntriesByType() function mentioned at the MDN link here - https://developer.mozilla.org/en-US/docs/Web/API/Performance/getEntriesByType. As per the link it mentions that the method returns a list of PerformanceEntry objects / empty list. However, when I invoke the "forEach" method on the returned value of the window.performance.getEntriesByType(type) method, I get the following error

TypeError: Object [object Object] has no method 'forEach'

Couple of doubts:

Why do I get the error 'forEach' has no method?
What does Object [object Object] in the error message imply?

Please edit your question to include your actual code. What browser are you using? — Jordan Running
– Jordan Running, Commented Feb 1, 2017 at 18:09

Scott Marcus · Accepted Answer · 2017-02-01 18:10:21Z

3

It means that you are attempting to invoke the forEach() method on an object that does not have forEach() method. forEach() is implemented on Array.prototype (meaning that all arrays have this method) and some browsers implement it on DOM nodeList objects. But, you are either trying to use it on another kind of object or in a browser that doesn't support it.

performance.getEntriesByType() returns a list, which is not the same thing as an Array, which is where forEach() is implemented.

The page you referenced, shows how you can loop through the resulting list from the window.performance.getEntriesByType() call.

  // Use getEntries() to iterate through the each entry
  var p = performance.getEntries();
  for (var i=0; i < p.length; i++) {
    log("Entry[" + i + "]");
    check_PerformanceEntry(p[i]);
  }

answered Feb 1, 2017 at 18:10

Scott Marcus

66k6 gold badges54 silver badges81 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Saint Over a year ago

Any help on why I see the error as Object [object Object]? Why the 3 object identifiers?

Scott Marcus Over a year ago

@Saint The default conversion of an object to a string is "[object Object]", so really you are just seeing the type of object you have an error with ("Object") and then the string representation of that, which shows it's underlying type as well ("[object Object]").

Jeff LaFay · Accepted Answer · 2017-11-21 14:58:57Z

1

I personally ran into a bug on an android device and the issue was in a dependency's code so I couldn't change it. I used this polyfill to fix the issue:

if (window.NodeList && !NodeList.prototype.forEach) {
    NodeList.prototype.forEach = function (callback, thisArg) {
        thisArg = thisArg || window;
        for (var i = 0; i < this.length; i++) {
            callback.call(thisArg, this[i], i, this);
        }
    };
}

answered Nov 21, 2017 at 14:58

Jeff LaFay

13.5k14 gold badges74 silver badges102 bronze badges

1 Comment

JakubK Over a year ago

Thanks @jlafay this polyfill made my Ionic 5 app work on my prehistoric Android 4.4 phone. I just had to change the way of checking if NodeList exists: if (window.hasOwnProperty('NodeList') && !NodeList.prototype.forEach)

Collectives™ on Stack Overflow

Javascript - TypeError: Object [object Object] has no method 'forEach'

2 Answers 2

2 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related