type Networkish: 
  | Network
  | number
  | bigint
  | string
  | {
  "chainId": number;
  "name": string;
};
A Networkish can be used to allude to a Network, by specifying:
  • A Network object
  • A well-known (or registered) network name
  • A well-known (or registered) chain ID
  • An object with sufficient details to describe a network

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Source

providers/network.ts:21