woocommerce-paypal-payments/modules/ppcp-settings/resources/js/utils/Helper/FormValidator.js

export default class FormValidator {
	constructor( url, nonce ) {
		this.url = url;
		this.nonce = nonce;
	}

	async validate( form ) {
		const formData = new FormData( form );

		const res = await fetch( this.url, {
			method: 'POST',
			headers: {
				'Content-Type': 'application/json',
			},
			credentials: 'same-origin',
			body: JSON.stringify( {
				nonce: this.nonce,
				form_encoded: new URLSearchParams( formData ).toString(),
			} ),
		} );

		const data = await res.json();

		if ( ! data.success ) {
			if ( data.data.refresh ) {
				jQuery( document.body ).trigger( 'update_checkout' );
			}

			if ( data.data.errors ) {
				return data.data.errors;
			}
			throw Error( data.data.message );
		}

		return [];
	}
}