Gas versus gas limit versus gas price
One of the most common concepts to get your head around is the the difference between gas, gas price, and gas limit. Knowing the difference between these different things is crucial. Let's start with gas.
Gas
Every transaction you do costs gas. What's gas? Well, it's the fuel needed to execute a transaction, denominated in Gwei, which is usually equal to 1*10-9 ETH. Recall the smallest denomination of ETH, wei, which is 1*10-18 ETH, that denominates the amount you will be paying for the transaction.
As we've seen before, you can specify a gas amount in a transaction. We've done this before using web3. Recall that in Chapter 6, Testing Your Dapp, we had the following line:
instance.reward(recipient, REWARD_WEI, { from: recipient, gas:3000000 })
As you can see, we specify a gas of 3000000.
We can also specify gas in our truffle.js file, as we've seen in Chapter 4, Migrating Your Dapp to Ethereum Blockchains:
// Allows us to use ES6 in our migrations and tests...
