How do I know if I am connecting to uniswap factory mainnet or testnet if the contract addresses are common for both?

Question

I had thought each contract deployment and contract address was unique on Ethereum, including across mainnet and testnets. But in the Uniswap documentation it says:

UniswapV2Factory is deployed at 0x5C69bEe701ef814a2B6a3EDD4B1652CB9cc5aA6f on the Ethereum mainnet, and the Ropsten, Rinkeby, Görli, and Kovan testnets. It was built from commit 8160750.

source: https://uniswap.org/docs/v2/smart-contracts/factory/

If this is the case, how can I choose whether I am connecting to the Uniswap mainnet or testnet factory contract? I am connecting via JavaScript and Truffle as follows:

      ...
  
      const UniswapContract = contract(UniswapFactoryAbi);
      UniswapContract.setProvider(this.web3);
      UniswapContract.at('0x5C69bEe701ef814a2B6a3EDD4B1652CB9cc5aA6f').then(function(instance) {

      ... 

Thanks in advance.

Answer 1

The network you are on depends on the provider you are using. In your case, this.web3 is associated with some that network that you defined earlier in the code. If you track down what network is associated with this.web3, you will know what Uniswap contract that is referring to.