JSON.stringify not adding commas between contained objects

Question

Although following the excellent information in https://stackoverflow.com/a/47116829/11308019 — especially the "Year 2018 answer" — I am trying to figure out a JSON.stringify problem. Example code follows...

const globAll = require('glob-all')
const fs = require('fs')
const cacheFile = '.base64imgs.json'

// clear cacheFile...
fs.writeFileSync(cacheFile,'')
let bCache = {}

files = globAll.sync([
  'src/images/*.jpg',
  'src/images/*.png',
])

files.forEach(file => {
  var bRes = `data for ${file} would go here`
  var bAdd = {file, bRes}
  bCache =  {...bCache, ...bAdd}
  fs.writeFileSync(cacheFile, JSON.stringify(bCache, null, 2), {flag: 'a'})
})

This results in output in .base64imgs.json like the following:

{
  "file": "src/images/1984-07-11_01_retouched_1280x720.jpg",
  "bRes": "data for src/images/1984-07-11_01_retouched_1280x720.jpg would go here"
}{
  "file": "src/images/2020-01-31--curmudgeonishish-2019_1280x726.jpg",
  "bRes": "data for src/images/2020-01-31--curmudgeonishish-2019_1280x726.jpg would go here"
}{
  "file": "src/images/alarm-clock-4711181_1280x853.jpg",
  "bRes": "data for src/images/alarm-clock-4711181_1280x853.jpg would go here"
}{
  "file": "src/images/almond-21502_1280x853.jpg",
  "bRes": "data for src/images/almond-21502_1280x853.jpg would go here"
}

...which obviously isn't valid JSON because there's no comma between the objects within the containing bCache object. (I also tried using arrays only, arrays within an object, objects within an array, etc.; same results each time.) I assume the fault is my own, but my days-long searches for answers in SO and other similar sources haven't shown me what I'm doing wrongly. So, any help and/or correction will be greatly appreciated!

Shouldn't bCache be an array rather than an object? so let bCache = []; and bCache = [...bCache, bAdd];. — Heretic Monkey
– Heretic Monkey, Commented Jun 5, 2020 at 20:49
@HereticMonkey did try all combos as noted in last paragraph. No joy. :-/ — Bryce Wray
– Bryce Wray, Commented Jun 5, 2020 at 20:51
Besides the array instead of object, part of your problem is using ...bAdd instead of just bAdd — Heretic Monkey shows it but doesn't mention it... you want to add the object, but with ...bAdd you are first expanding bAdd with the spread operator and adding the expansion to bCache. — Stephen P
– Stephen P, Commented Jun 5, 2020 at 21:04
@HereticMonkey --- from what the others said below, looks as if I should've listened to you in the first place. Thanks. — Bryce Wray
– Bryce Wray, Commented Jun 5, 2020 at 21:04

JstnPwll · Accepted Answer · 2020-06-05 20:55:32Z

2

You'll want to use an array instead of an object for bCache. And you should probably write out all at once instead of appending in a loop.

let bCache = []
let files = ['file 1','file 2','file 3']

files.forEach(file => {
  var bRes = `data for ${file} would go here`
  var bAdd = {file, bRes}
  bCache = [...bCache, bAdd]
})
console.log(JSON.stringify(bCache, null, 2))

answered Jun 5, 2020 at 20:55

JstnPwll

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Bryce Wray Over a year ago

Thanks. Looks like that'll do it. Marked as answer.

Barmar · Accepted Answer · 2020-06-05 21:00:14Z

1

Don't write the JSON inside the loop. Create an array of all the data, and write it once at the end of the loop.

const globAll = require('glob-all')
const fs = require('fs')
const cacheFile = '.base64imgs.json'

files = globAll.sync([
  'src/images/*.jpg',
  'src/images/*.png',
])

bCache = files.map(file => {
  var bRes = `data for ${file} would go here`
  return {file, bRes}
});

fs.writeFileSync(cacheFile, JSON.stringify(bCache, null, 2));

answered Jun 5, 2020 at 21:00

Barmar

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