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msonnabaum/reduce_wtf.js

Created November 10, 2015 21:48
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reduce_wtf.js
[1,2,3].reduce(function(memo, current) {
console.log(memo);
}, {});
// > {}
// > undefined
// > undefined
@mikeyp
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mikeyp commented Nov 10, 2015

memo is based on the return value which is empty, try

[1,2,3].reduce(function(memo, current) {
  console.log(memo);
  return memo;
}, {});

@Thiruppathi
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When using reduce follow the 2 rules.

  1. Always pass an initialValue
  2. Always return the accumulator
var data = [1,2,3];
var initialValue = 0;
var reducer = function(accumulator, item) {
  return accumulator + item;
};
var total = data.reduce(reducer, initialValue);
console.log('Sum of the array', data, 'is: ', total);

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