Object doesn't support property or method 'entries'

2/10/2020 UPDATE: Like @Monomachus said, first try adding this line to polyfill.ts:

import 'core-js/es7/object';

If this fixes it, make sure to give his answer credit! If needed, you can manually define it using the instructions below:

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Original Response: Essentially, a polyfill is a way you can manually define a function that isn't natively supported on a specific platform/browser.

In your case, there is a basic definition of the function Object.entries given here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/entries#Polyfill

They provide this simple, ready to deploy definition:

if (!Object.entries)
  Object.entries = function( obj ){
    var ownProps = Object.keys( obj ),
        i = ownProps.length,
        resArray = new Array(i); // preallocate the Array
    while (i--)
      resArray[i] = [ownProps[i], obj[ownProps[i]]];

    return resArray;
  };

Looking at the code above, the first thing it checks is if Object.entries exists. If it does, no worries, but if it doesn't exist, then it creates it... As long as this function gets defined before you actually call it in your code, you should be fine.

Using something like angular-cli, they provide a polyfills.ts file (which gets executed before your app is run) where you can place code like this or import files containing definitions you'll need.

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10/30/2018 UPDATE:

@apsillers correctly pointed out the answer above does not apply to FormData.entries(), but to Object.entries() instead.

Solution for FormData.entries() (this worked for me): https://stackoverflow.com/a/49556416/3806701

Basically, import this poly-fill:

<script src="https://unpkg.com/formdata-polyfill"></script>

Then you can iterate FormData as follows:

var formDataEntries = (<any>formData).entries(), formDataEntry = formDataEntries.next(), pair;
while (!formDataEntry.done) {
    pair = formDataEntry.value;
    console.log(pair[0] + ', ' + pair[1]);
    formDataEntry = formDataEntries.next();
}

If you're in an Angular App please add this line to your polyfills.ts file

import 'core-js/es7/object';

It will import all the new methods on Object, including entries

By importing

import 'core-js/es7/object';

if you are getting error

Module not found: Error: Can't resolve 'core-js/es7/object'

then Change all "es6" and "es7" to "es" in your imports.

import 'core-js/es/object';