Technical Overview

As stated in the introduction, eosjs integrates with EOSIO-based blockchains using the EOSIO Nodeos RPC API.

In general, there are two objects that are used to interact with a blockchain via eosjs: the JsonRpc object, and the Api object.


The JsonRpc object is typically used when signing is not necessary. Some examples include getting block information, getting transaction information, or getting table information.

The requests made by the JsonRpc object will either use a built-in fetch library, or the fetch library passed in by the user to issue requests to the endpoint specified when instantiating the JsonRpc object. When the various methods (get_abi, get_account, get_block_header_state, etc) of the JsonRpc object are invoked, the calls are delegated to the JsonRpc object's fetch function, which in turn, delegate the requests to the fetch library.


The Api object is typically used when transacting on an EOSIO-based blockchain. Some examples include staking, creating an account, or proposing multi-sig transactions.

The typical use of the Api object is to call its transact method. This method performs a number of steps depending on the input passed to it:

  • The transact method first checks if the chainId was set in the Api constructor, and if not, uses the JsonRpc object's get_info method to retrieve the chainId.
  • The transact method then checks if the expireSeconds and either blocksBehind or useLastIrreversible fields are set and well-formed in the optional configuration object, as specified in How to Submit a Transaction.

    • If so, either the last_irreversible_block_num or the block blocksBehind the head block retrieved from JsonRpc's get_info is set as the reference block and the transaction header is serialized using this reference block and the expireSeconds field.
  • The transact method then checks if the appropriate TAPOS fields are present in the transaction (they can either be specified directly in the transaction or in the optional configuration object) and throws an Error if not.
  • The necessary abis for a transaction are then retrieved for the case when transact is expected to sign the transaction.
  • The actions are serialized using the eosjs-serialize ser object.
  • The entire transaction is then serialized, also using the eosjs-serialize ser object.
  • The transaction is then optionally signed, using the signatureProvider, the previously retrieved abis, the private keys of the signatureProvider, and the chainId.
  • The transaction is then optionally compressed, using the deflate function of a Javascript zlib library.
  • The transaction is then optionally broadcasted using JsonRpc's push_transaction.