Following a tutorial but can't figure out why I'm getting this message: "Property 'substring' does not exist on type '() => WordArray'.ts(2339)"

Question

I'm a beginner following a yt blockchain tutorial on visual code yet i'm getting this message when using substring: Property 'substring' does not exist on type '() => WordArray'.ts(2339)

class Block {
    constructor(index, timestamp, data, previousHash = ''){
        this.index = index;
        this.timestamp = timestamp;
        this.data = data;
        this.previousHash = previousHash;
        this.hash = this.calculateHash;
        this.nonce = 0;
    }

    calculateHash(){
        return SHA256(this.index + this.previousHash + this.timestamp + JSON.stringify(this.data) + this.nonce.toString());

    }

    mineBlock(difficulty){
        while(this.hash().substring(0, difficulty) !== Array(difficulty + 1).join("0")){
            this.nonce++;
            this.hash = this.calculateHash();
        }
    
        console.log("Block mined: " + this.hash);
    }

}

Answer 1

this.hash is a function that returns some kind of list. There is no substring method on the function itself, only on the result.

You need to use this.hash() to call the function to get its result. Then this.hash().substring might work.

Answer 2

The issue is you are trying to use substring method on a non String class. I'm going to assume you're using the CryptoJS implementation of SHA256 given the capitalization. If not I'll delete the answer, but you need to convert the hash to a String class in order to use the substring method. The SHA256 does not return a string and you need to convert it to one in order to apply string methods to it. Changing the calculateHash method to this should make the code work:

calculateHash(){
  return SHA256(this.index + this.previousHash + this.timestamp + JSON.stringify(this.data) + this.nonce.toString()).toString();
  }

More info can be found in the docs