Vue problem when trying to access the clientWidth and clientHeight refs of the DOM

Property 'clientWidth' does not exist on type 'Vue | Element | Vue[] | Element[]'.
Property 'clientHeight' does not exist on type 'Vue | Element | Vue[] | Element[]'.

<div class="invoice-step-detail" id="invoice" ref="invoice">

@Component({
    name: 'CreateInvoice',
    components: { }
})
export default class CreateInvoice extends Vue {

downloadPdf(){
        let pdf = new jsPDF("p", "pt", "a4", true);
        let invoice = document.getElementById('invoice');
        let width = this.$refs.invoice.clientWidth;
        let height = this.$refs.invoice.clientHeight;

        html2canvas(invoice!).then(canvas => {
            let image = canvas.toDataURL('image/png');
            pdf.addImage(image, 'PNG', 0, 0, width * 0.55, height * 0.55);
            pdf.save('invoice');
        })
    }
async submitInvoice(): Promise<void> {
        this.invoice = {
            createdOn: new Date,
            updatedOn: new Date,
            customerId: this.selectedCustomerId,
            lineItems: this.lineItems,
        };
        await invoiceService.makeNewInvoice(this.invoice);

        this.downloadPdf();
        await this.$router.push("/orders");
    }
}

Any suggestions? I'm still new in vue and the weird thing is that this code works this way but it trows that error.