WETH Gateway

If you need to use native ETH in the protocol, it must first be wrapped into WETH. The WETH Gateway contract is a helper contract to easily wrap and unwrap ETH as necessary when interacting with the protocol, since ETH is no longer used within protocol interactions.
The source code can be found here, with the latest deployed address listed in the Deployed Contracts.
Methods
depositETH()
function depositETH(address onBehalfOf, uint16 referralCode)
Deposits the msg.value amount of ETH into the protocol, minting the same amount of corresponding aWETH, and transferring them to the onBehalfOf address.
For referralCode input explanations, please refer to the referral program section of the documentation. During testing, you can use the referral code: 0.
Ensure that the depositETH() transaction also includes the amount of ETH you are depositing in the msg.value.
Parameter Name
Type
Description
onBehalfOf
address
address whom will receive the aWETH. 
Use msg.sender when the aTokens should be sent to the caller.
referralCode
uint16
referral code for our referral program. Use 0 for no referral.
withdrawETH()
function withdrawETH(uint256 amount, address to)
Withdraws amount of the WETH, unwraps it to ETH, and transfers the ETH to the to address.
Ensure you set the relevant ERC20 allowance of aWETH, before calling this function, so the WETHGateway contract can burn the associated aWETH.
Parameter Name
Type
Description
amount
uint256
amount deposited, expressed in wei units. 
Use type(uint).max to withdraw the entire balance.
to
address
address that will receive the unwrapped ETH
repayETH()
function repayETH(uint256 amount, uint256 rateMode, address onBehalfOf)
Repays onBehalfOf's debt amount of ETH which has a rateMode.
Ensure that the repayETH() transaction also includes the amount of ETH you are repaying in the msg.value.
Parameter Name
Type
Description
amount
uint256
amount to be borrowed, expressed in wei units.
Use uint(-1) to repay the entire debt,  ONLY when the repayment is not executed on behalf of a 3rd party. 
In case of repayments on behalf of another user, it's recommended to send an _amount slightly higher than the current borrowed amount.
rateMode
uint256
the type of borrow debt.
Stable: 1, Variable: 2
onBehalfOf
address
address of user who will incur the debt.
Use msg.sender when not calling on behalf of a different user.
borrowETH()
function borrowETH(uint256 amount, uint256 interestRateMode, uint16 referralCode)
Borrows amount of WETH with interestRateMode, sending the amount of unwrapped WETH to msg.sender.
Parameter Name
Type
Description
amount
uint256
amount to be borrowed, expressed in wei units
interestRateMode
uint256
the type of borrow debt.
Stable: 1, Variable: 2
referralCode
uint16
referral code for our referral program. Use 0 for no referral code.
View Methods
getWETHAddress()
function getWETHAddress()
Returns the WETH address used by the WETHGateway.
getAWETHAddress()
function getAWETHAddress()
Returns the aWETH address used by the WETHGateway.
getLendingPoolAddress()
function getLendingPoolAddress()
Returns the LendingPool address used by the WETHGateway.
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Parameter Name	Type	Description
`onBehalfOf`	address	address whom will receive the aWETH. Use `msg.sender` when the aTokens should be sent to the caller.
`referralCode`	uint16	referral code for our referral program. Use 0 for no referral.