Ajax - Filter by price in Shopify / Liquid

I have a collection which I want to be able to filter (not sort) products by price. I do not want to use an app.

I am aware of this question Add price filter in shopify? however this is not what I am looking for; I want to be able to choose any combination of numbers e.g. between $4 and $20, or $7 and $30, etc, that the user can change, not just a predetermined range. I have seen it done on a Shopify site and therefore know it can be done. I believe this will require ajax calls.

An answer would be extremely helpful both to myself and to many others as this seems to be a very basic requirement which remains unanswered on SO / Shopify forums, even if just a general instruction rather than any specific code. For reference I am using the default (debut) theme.

My project is similar to yours so fill in the blank below.

create a collection template collection.price-filter.liquid
use ajax to get the products json. of course there is a limit of 250. If you have more than 250 then needed to use an app to filter the result first. or, just use multiple request.

<script>
    var allProducts;
    var filteredProducts = [];
    var activeFilter = [];
    $(document).ready(function(){
        var url = '{{collection.url}}/products.json?limit=250';
        const res = getProducts(url);
    });

    function getProducts(url){
        $.ajax({
            type: 'GET',
            url: url,
            success: function(res){ 

                allProducts = res.products;
                filterProducts(allProducts);
            },
            error: function(status){
                 alert(status);
            }
        });
    }
</script>

filter the product to fill in filteredProducts array objects

//loop through the products, create categories ($20-$40, $40-$60, etc.)
function filterProducts(products){
    var cat1 = '20-40', cat2 = '40-60';
    var currentCat;
    products.forEach(function (i, j){   
        if (i.price > 20 && i.price <= 40){
            currentCat = cat1;
        else if (i.price > 40 && i.price <= 60) {
            currentCat = cat2;
        }
            if(filteredProducts[currentCat]){
                filteredProducts[currentCat].push(i);
            }
            else {
                filteredProducts[currentCat] = [i]
            }
        };
    });
}

After generated filteredProducts, listen to checkbox selection from User, add the selection into an array called activeFilter

function getActiveFilter(){
    $('#myFilter').each(function(){
        if($(this).is(':checked')){
            //add to activeFilter
        }
    });
}

Generate resultFilter from filteredProducts and activeFilter, eliminate common result;

function resultFilter(){
    var result = [];
    activeFilter.forEach(function (i, value){
        Object.keys(value).forEach(function(j, product){
            //add to result
        };
    });
}

Build/show product result using handlebars.js

<script id="ProductTemplate" type="text/x-handlebars-template">
  {% raw %}
    {{#product}}
        <div class="col">
          <a href="/products/{{productHandle}}" class="grid__image">
            <div class="product__image-wrapper" style="background-color: white;">
              <img class="no-js lazyload" width="316" height="237"
                data-src="{{ featuredImg }}"
                data-widths="[108, 360, 375, 414, 568, 684, 720, 732, 736, 768, 1024, 1200, 1296, 1512, 1728, 1944, 2048]"
                data-aspectratio="1.33"
                data-sizes="auto"
                data-parent-fit="width"
                alt="{{ title }}">
            </div>
          </a>
          <p class="h5"><a href="/products/{{productHandle}}">{{ title }}</a></p>
        </div>
    {{/product}}
   {% endraw %}
</script>

Insert data into #container-products, where you want the filtered Products to show.

function buildFilteredProducts(filteredProds) {
        var $productContainer = $('#container-product');
        $productContainer.empty();
        if(filteredProds.length <= 0){
            $productContainer.append('empty result');
            return;
        }

        var products = [];
        var product = {};
        var data = {};
        var source = $("#ProductTemplate").html();
        var template = Handlebars.compile(source);
        products = filteredProds.map(function(productItem) {
            return product = {
            id: productItem.id, 
            title: decodeHtml(productItem.title),
            featuredImg: responsiveImage(productItem.images[0].src),
            productHandle: productItem.handle
            }
        });

        data = {
            product: products
        } 

        $productContainer.append(template(data)); 
    }