Mining implies the block will be added?

[lbragile]

When mining, shouldn't the solutionHash be compared to a targetHash and the block only be added if solutionHash <= targetHash?

Otherwise, what stops a miner from having a list of predefined hashes that meet the criteria of having 4 leading zeros and just submitting them.

On that note, it would also make more sense to have a variable number of leading zeros in the mining process' expected solution hash for each block that needs to be added to the chain.

I am currently working on a project similar to this to get a better understanding in the cryptocurrency space.
Feel free to have a look and let me know if the above is indeed correct and I will make a PR

[NYC00kie]

Otherwise, what stops a miner from having a list of predefined hashes that meet the criteria of having 4 leading zeros and just submitting them.

Other miners will need to confirm that the submitted hash is actually the correct hash.
That is how the Blocks are confirmed in a decentral manner.
If the hash cannot be confirmed with the submitted solution then it wont get integrated into the Blockchain.