How to use Proj4 in OfficeScript

proj4.OfficeScript.ts

type Proj4 = (from: string, to: string, coords: [number, number]) => [number, number];
let loadedProj4 = false;
async function getProj4(): Promise<Proj4> {
    if (!loadedProj4) {
        const r = await fetch("https://cdnjs.cloudflare.com/ajax/libs/proj4js/2.19.10/proj4.js");
        new Function(await r.text())();
        loadedProj4 = true;
    }
    return (globalThis as { proj4?: Proj4 }).proj4;
}

async function main(workbook: ExcelScript.Workbook) {
    // Get the active cell and worksheet.
    const selectedCell = workbook.getActiveCell();
    const proj4 = await getProj4()
    const [x, y] = proj4('EPSG:4326', 'EPSG:3857', [-0.1278, 51.5074]);
    selectedCell.setValue(x)
    
}