I have this array of movies, I'm trying to use the reduce function and the expected output should be: 420(the total duration of the 3 objects), the output I'm getting right now is like a concatenation of the 3 strings, why is that?
let movies = [ { 'name': 'Jumanji', 'duration': 120 }, { 'name': 'Harry Potter', 'duration': 60 }, { 'name': 'Toy Story', 'duration': 240 } ]; let newAr = movies.reduce((previousValue, currentValue) => [ previousValue + currentValue.duration ], []); console.log('newAr', newAr)
The previousValue
will be the accumulator, the value returned by the prior iteration of the callback - or, the initial value - so it'll be an array. Doing someArray + someOtherValue
will coerce the array into a string (in other words, doing .join(',')
) and concatenate it with the expression on the right.
I'd map the movies to their durations instead, then add them up:
const totalDuration = movies
.map(m => m.duration)
.reduce((a, b) => a + b, 0);
Or do it in one step, though it might be a bit harder to parse at a glance if you're unfamiliar with reduce
.
const totalDuration = movies
.reduce((a, movie) => a + movie.duration, 0);
const movies = [ { 'name': 'Jumanji', 'duration': 120 }, { 'name': 'Harry Potter', 'duration': 60 }, { 'name': 'Toy Story', 'duration': 240 } ]; console.log(movies.reduce((previousValue, currentValue) => previousValue + currentValue.duration, 0))
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