How to call external payable contract function from app.js (DApp)?

Question

The contract has a function:

function purchaseTokens() external payable {
    require(msg.value>0);
    ...etceteras...
}

What I need is an app.js part, something that would look like this (lets say I want to hard-code 12 wei for a deposit):

purchaseTokens : function (){
    App.contracts.name_of_contract.deployed().then(async function(instance){
        let message = await instance.purchaseTokens.call('12');
        App.showMessage(message);
    }).catch((err) =>{
        App.showError(err);
    })
},

However, the js function returns: TypeError: Cannot read property 'toString' of null.

What should I do for the app.js part ?

Answer 1

I'm not the strongest player in this dialect, but this looks familier:

await instance.purchaseTokens.call('12');

Try adding transaction arguments (gas, gasPrice, value) like this:

await instance.purchaseTokens.call({value: <amount>});

call is probably wrong, so:

`await instance.purchaseTokens({value: });

Hope it helps.

p.s. If there are arguments for the function and you also want transaction arguments:

instance.function(arg1, arg2, {gas: <qty>, value: <amount>});