undefined properties not being added to object-CodePudding

I have the following code:

let object = {};
Object.keys(this.graphQL.body).forEach((key) => {
    console.log(key, this[key])
    object[key] = this[key]
})
let json = JSON.stringify(object);
console.log('API json', json)

Which gives this out this console log:

id undefined
title undefined
filename mitchel-lensink-Y2OCQVuz6XM-unsplash.jpg
description undefined
keywords undefined
assetID undefined
height undefined
width undefined
uploadOwnerType image
uploadOwnerID 100513
createdAt undefined
updatedAt undefined
API json {"filename":"mitchel-lensink-Y2OCQVuz6XM-unsplash.jpg","uploadOwnerType":"image","uploadOwnerID":100513}

Why do I not get the undefined keys added? And how can I add them anyway?

CodePudding user response：

JSON.stringify method removes undefined keys by default.

let json = JSON.stringify(object);

To keep these, we can use a replacer -

let object = {};
Object.keys(this.graphQL.body).forEach((key) => {
    console.log(key, this[key])
    object[key] = this[key]
})

const replacer = (key, value) =>
  typeof value === 'undefined' ? null : value;

let json = JSON.stringify(object, replacer);
console.log('API json', json)

Let me know in the comments if need any further elaboration.

CodePudding user response：

Undefined keys are added but JSON.stringify omits all fields with undefined values. To add undefined valued keys you can use replacer function:

const replacer = (key, value) =>
  typeof value === 'undefined' ? null : value;

And then send this as second parameter to JSON.stringify function

let json = JSON.stringify(object, replacer);

Check this blog post for more information: https://muffinman.io/blog/json-stringify-removes-undefined/