将此参数和第二个参数传递给回调函数

Question

I have a JSCS rule that identifies functions within for loops. I'm wanting to adhere to the rule vs turn off the warning. This is the code in the JSCS error state.

let sum = 0;
for (var key in denomGroup) {
    denomGroup[key].forEach(function (denom) {
        sum = addToSum(sum, denom)
    });
}
return sum;

I've tried this below and the addToSum function gets the object, but I can't figure out how to pass in the sum and have it iterate and continue to add other values

for (var key in denomGroup) {
    denomGroup[key].forEach(addToSum);
} 

function addToSum(denom, sum) { //denom has object, sum is empty
    return sum += denom.sum;
}

I've also tried

for (var key in denomGroup) {
    denomGroup[key].forEach(addToSum(sum));
} 

function addToSum(sum, denom) { //sum has 0, denom is empty
    return sum += denom.sum;
}

How can I correctly call an outside function with the intent of the first code block? I need to avoid just placing sum as a global variable.

Answer 1

You don't need to pass the sum to the function, simply declare the function within the same scope as you declare sum :

 let sum = 0; let denomGroup = { a: [1,2,3], b: [4,5,6] }; function addToSum(denom) { return sum += denom; } for (var key in denomGroup) { denomGroup[key].forEach(addToSum); } console.log(sum); 

EDIT: as @ScottMarcus points out, the sum variable doesn't need to be global, just in the same (or a higher) scope as the function definition. You could, for example, encapsulate the whole thing as so:

 function countDenoms(denomGroup) { let sum = 0; function addToSum(denom) { sum += denom; } for (var key in denomGroup) { denomGroup[key].forEach(addToSum); } return sum } console.log(countDenoms({ a: [1, 2, 3], b: [4, 5, 6] }));