then-able javascript function example

promise_ex.js

/*
* An example of a function fetching data
* and returning a promise, making itself
* "thenable".
ref: https://scotch.io/@wesleylhandy/writing-your-own-javascript-promises
*/
function fetchIds(url) {
    return new Promise((resolve, reject) => {
        
        queryUrl = "/query?f=json&where=1%3D1&returnIdsOnly=true"
        fetch(url + queryUrl)
            .then(function (response) {
                return response.json();
            })
            .then(function (data) {
                //return new Promise(function (resolve, reject) {
                    resolve(data.objectIds)
            })
            .catch(function (err) {
                console.log(err);
                console.log("something went south");
                reject(err);
            })
    });
}

function countRecords() {
    var url = "https://services.arcgis.com/P3ePLMYs2RVChkJx/arcgis/rest/services/USA_Major_Cities/FeatureServer/0"
    fetchIds(url).then(function (ids) {
            console.log(ids.length)
        })
}

Actually fetch() might need ES5