Autosaving forms

autosave.js

//call fieldUpdate() as the handler for oninput on your form
function fieldUpdate(){
    const formData = {};
    const inputs = Array.of(...document.querySelectorAll("input")).filter(it => it.type !== "submit")
    inputs.forEach(it => formData[it.id || it.name] = it.value)
    window.localStorage.setItem("formData", JSON.stringify(formData))
}

function load(){
    const formData = JSON.parse(window.localStorage.getItem("formData"))
    const fields = Object.entries(formData)
        .map( ([k,v]) => {
            id = document.getElementById(k);
            return [id ? id : Array.of(...document.querySelectorAll(`input[name="${k}"]`)), v]
        })
    fields.forEach( ([elems, value]) => elems.forEach(elem => elem.value = value) )
}

load();