collection.js

if(window.location.pathname.includes("/collections")) {
    (async () => {
        const meta = await fetch("https://www.kasper.com/collections/clothing?view=meta").then(response => response.text()).then(response => JSON.parse(response));

        const products = (await Promise.all(Array.from(new Array(meta.pages).keys()).map(page => page + 1).map((page) => {
            return fetch(`https://www.kasper.com/collections/clothing/products.json?page=${page}`).then(response => response.json());
        }))).map(products => products.products).reduce((result, products) => {
            return [
                ...result,
                ...products,
            ];
        }, []);

        console.log(products);
    })();
}

collection.meta.liquid

{%- layout none -%}
{%- assign products_count         = collection.products_count -%}
{%- assign pages                  = products_count | divided_by: 30 -%}
{%- assign products_count_modulo  = products_count | modulo: 30 -%}
{%- if products_count_modulo > 0 -%}
  {%- assign pages = pages | plus: 1 -%}
{%- endif -%}
{%- capture meta_json -%}
{
  "total": {{- products_count | json -}},
  "pages": {{- pages -}}
}
{%- endcapture -%}
{{- meta_json -}}