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Start your free trialSamuel Kleos
Front End Web Development Techdegree Student 13,679 PointsWhat if... 🤔 these two methods are the same. Then is it true .reduce() is just performing a variable assignment?
const acc = {}; // this assignment is the same as.. (see next comment) 👇🏽
for (let item of users) {
acc[item.name] = item.age;
}
const assignedAges = users.reduce((acc, item) => {
acc[item.name] = item.age;
return acc;
}, {}) // making the assignment here?
Therefore acc is just a constant that needs to be returned every time the multi-line callback (wrapped in braces) does a loop through each element?
1 Answer
Steven Parker
231,272 PointsThe optional 2nd argument to a callback is indeed assigned to the accumulator before the callback is used.
The main difference between these two examples is that "acc" in the first case is a constant but in the second case it is a function parameter.
Samuel Kleos
Front End Web Development Techdegree Student 13,679 PointsSamuel Kleos
Front End Web Development Techdegree Student 13,679 PointsSo effectively,
acc
in the second example is first declared as a variable in the parameter of the callback, and then assigned a value in the second parameter of the .reduce() method?Steven Parker
231,272 PointsSteven Parker
231,272 PointsEssentially, but normally the word "variable" is not used to refer to a parameter. It would be more common to just say that it is "declared as a parameter of the callback".