Row creation in Javascript is easy ...

ACF Repeater creation

/**
 * Use this gist to add a row in a repeater field and retrieve all the sub fields you can manage later.
 *
 * @author     : Christian Denat
 * @email      : [email protected] / [email protected]
 *
 * @date       : 20210525
 *
 */

// Get repeater field (replace my-repeater-field-key' with a field key)
repeater = acf.getField('my-repeater-field-key');

// Add a new row
$row = repeater.add();

// Get subfields
let sub_fields=acf.getFields({parent: $row});

// show sub fields                    
console.log(sub_fields);

// loop around sub fields and populate them.