Unexpected token u in JSON at position 0

This error occurs when I use node.js to write some to get the response of an API with JSON format. It's OK when use the response as string but JSON.parse it occurs. The first thing I do is to check the content of raw content I find some Chinese chars and also Googled some articles saying like \u unicode chars may break the parse function. I checked all raw content string but not found any one. Then I check the stdout to see where it broken, and found after a Chinese series string block there is a \n, so I use string.replace(/\n/g, raw) to trim all \n to make it work. But I'm wrong, it also breaks!

I'm confused why it can not run!

This time I google Unexpected token u in JSON at position 0 and get a result say:

Unexpected token u in JSON at position 0 because of JSON.parse 's input parameter is undefined

It's a very important hint for me, then I check the raw type use typeof

console.log(typeof raw)

It output to console as what I want:

string

But it also fails and why? Then I focus on the raw declaration:

let raw

Yeah you know it's not given any kind of value, so that time you try to typeof it you'll get undefined. Maybe it's a bug? If you give it a empty string value to initialize it, is it OK?

let raw = ''

Great, that's it!

Even I check its type before use JSON.parse and get the string type but failed to use JSON.parse

console.log(typeof raw)
console.log(JSON.parse(raw))