Size of json object? (in KBs/MBs)

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An answer to the actual question should include the bytes spent on the headers and should include taking gzip compression into account, but I will ignore those things.

You have a few options. They all output the same answer when run:

If Using a Browser or Node (Not IE)

const size = new TextEncoder().encode(JSON.stringify(obj)).length
const kiloBytes = size / 1024;
const megaBytes = kiloBytes / 1024;

If you need it to work on IE, you can use a pollyfill

If Using Node

const size = Buffer.byteLength(JSON.stringify(obj))

(which is the same as Buffer.byteLength(JSON.stringify(obj), "utf8")).

Shortcut That Works in IE, Modern Browsers, and Node

const size = encodeURI(JSON.stringify(obj)).split(/%..|./).length - 1;

That last solution will work in almost every case, but that last solution will throw a URIError: URI malformed exception if you feed it input containing a string that should not exist, like let obj = { partOfAnEmoji: "👍🏽"[1] }. The other two solutions I provided will not have that weakness.

(Credits: Credit for the first solution goes here.
Credit for the second solution goes to the utf8-byte-length package (which is good, you could use that instead).
Most of the credit for that last solution goes to here, but I simplified it a bit.
I found the test suite of the utf8-byte-length package super helpful, when researching this.)

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