SCALABLE: Save form data to localStorage and auto-complete on refresh

script.js

// With the help of Jeremy Keith, I was able to create a fully scalable code sample that you can copy-paste into your project.
// It will save the user input value on blur, this includes radio buttons, checkboxes and date inputs besides regular text/number inputs.
// The only condition is that you give the form element on your page a data-attribute of data-form-topic="foo".
// This code snippet saves the data-attribute as the key to the localStorage, and the value of it will be an object with key/value pairs of the respective inputs name and value.
// Please refer to this gist somewhere in your code if you use it :)
// Happy coding!

// VARIABLE DECLARATIONS
// objects
let savedData = {};
let autocompletedData;

// HTML elements
const inputs = document.getElementsByTagName("input");

document.addEventListener("DOMContentLoaded", () => {
    const form = document.querySelector("form");

    if (window.localStorage) {
        if (!form) {
            return;
        }

        if (!form.dataset.formTopic) {
            return;
        }

        let getFormTopic = localStorage.getItem(form.dataset.formTopic);
        if (!getFormTopic) {
            return;
        }
        autocompletedData = JSON.parse(getFormTopic);

        var formTopic = form.dataset.formTopic;
        console.log(formTopic);

        function getKeyValue() {
            for (const dataKey in autocompletedData) {
                let value = autocompletedData[dataKey];

                let formField = document.querySelector(
                    "[name = " + dataKey + "]"
                );

                switch (formField.type) {
                    case "radio":
                        formField = document.querySelector(
                            `input[name = '${dataKey}'][value = '${value}']`
                        );
                        formField.setAttribute("checked", "checked");
                        break;
                    case "checkbox":
                        formField.setAttribute("checked", "checked");
                        break;
                    case "file":
                        break;
                    default:
                        formField.value = value;
                }
            }
        }

        getKeyValue();
    }
});

if (window.localStorage) {
    function saveFormDataToLocalStorage(e) {
        const form = e.target.closest("form");
        let submitData = new FormData(form);

        for (let [dataKey, value] of submitData.entries()) {
            savedData[dataKey] = value;
            console.log(dataKey, value);
        }

        window.localStorage.setItem(
            form.dataset.formTopic,
            JSON.stringify(savedData)
        );
    }

    Array.prototype.forEach.call(inputs, function (input) {
        switch (input.type) {
        }

        input.addEventListener("blur", function (e) {
            e.preventDefault();

            saveFormDataToLocalStorage(e);
        });
    });
}