How can I save a json value from HTML/JavaScript in a json file locally without plugin?

I want to save some numbers from a small program in a local JSON file.


const increaseButton = document.getElementById("increase-button")
const numberField = document.getElementById("count-field")
let myNum = 0
let myArray = []
increaseButton.addEventListener("click", increaseNum)

function increaseNum() {
    numberField.innerText = myNum
    let jsonString = JSON.stringify(Object.assign({}, myArray))

The jsonString should be saved in a local file “myjson.json”.

Goal: If I increase the number with the increaseButton, the new value should be saved in the “myjson.json” file:

    "numbers": {

The only option I found was with node.js plugin “fs” and a lot of code. Couldn’t it be easier?


No, it can’t be done with a file if you want to save it locally. You could, however, save it to the localStorage:

// To save
localStorage.setItem('numbers', jsonString)

// To read
const jsonString = localStorage.getItem('numbers') || '';
const obj = JSON.parse(jsonString);


When I restart the browser is the value saved?

At the top of my head I’d think you could either create a upload/download option thus manually handle the file.
OR you could turn the data into a cookie and save it in the browser that way.

I think browsers in general are a bit iffy about just writing and reading files on the computer without explicit control of the user. You know, because of malware.


Sounds sensible but FCC is storing data in ls (and all the rest), at least I can access it from the console or from storage tab, and don’t remember them asking…

@BigBang localStorage seems to be persistent if you close the page. If using incognito mode it doesn’t though.

sessionStorage instead, disappears when page is closed.

Edit: also this mdn tutorial seems good start


Yes if you save it in the local storage, it would remain there unless you delete it.

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