Covert list of records in to csv download format

import { LightningElement, api, wire, track } from 'lwc';
import retrieveContacts from '@salesforce/apex/downloadContcatApexClass.retrieveContactMethod';
export default class DownloadContacts extends LightningElement {
    @api recordId;
    @track contacts;
    @track error;
    @api invoke(){
        retrieveContacts({ recordIdAccount: this.recordId })
            .then((result) => {
                console.log('line 12:' + result);
                this.contacts = result;
                this.error = undefined;
            })
            .catch((error) => {
                this.error = error;
                this.contacts = undefined;
            });
        var columnEnd = ',';
        var lineEnd = '\n';
        // Get the CSV header from the list.
        var keys = new Set();
        this.contacts.forEach(function (record) {
            Object.keys(record).forEach(function (key) {
                keys.add(key);
            });
        });
        keys = Array.from(keys);
        var csvString = '';
        csvString += keys.join(columnEnd);
        csvString += lineEnd;
        for (var i = 0; i < this.contacts.length; i++) {
            var counter = 0;
            for (var sTempkey in keys) {
                var skey = keys[sTempkey];
                // add , after every value except the first.
                if (counter > 0) {
                    csvString += columnEnd;
                }
                // If the column is undefined, leave it as blank in the CSV file.
                var value = this.contacts[i][skey] === undefined ? '' : this.contacts[i][skey];
                csvString += '"' + value + '"';
                counter++;
            }
            csvString += lineEnd;
            var hiddenElement = document.createElement('a');
            hiddenElement.href = 'data:text/csv;charset=utf-8,' + encodeURI(csv);
            hiddenElement.target = '_self';
            //hiddenElement.download = component.get("v.fileName");
            document.body.appendChild(hiddenElement); //Required for FireFox browser
            hiddenElement.click(); // using click() js function to download csv file
        }
    }
}

I have to create lwc quick action to convert related contacts in to csv download. i had  created lwc quick action button and retrieved the data needed.there is problem in converting to csv. I have tried everything .below is my code. thanks in advance for any help.please help.

ERROR :-Cannot read properties of undefined (reading 'forEach')

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