在 JavaScript 中使用 reduce 来展平阵列

Question

I'm getting a little confused with using reduce.

it's array.reduce((accumulator, value) => do something with accumulator, why is this returning back an empty array?

 let a = [ [1,2], [ [3,4] ], [ [[5],[6]] ] ]; const flatten = arr => arr.reduce((a, v) => { v instanceof Array? flatten(v): a.push(v); return a; }, []) console.log(flatten(a));

Answer 1

The flatten(v) returns an array, but you're not doing anything with it currently. Try pushing the spread array into the accumulator instead:

 let a = [ [1,2], [ [3,4] ], [ [[5],[6]] ] ]; const flatten = arr => arr.reduce((a, v) => { v instanceof Array ? a.push(...flatten(v)) : a.push(v); return a; }, []) console.log(flatten(a));

Or, you can use concat , and only use the conditional operator when you need the entire thing to resolve to an expression (don't use it as an alternative to if / else ):

 let a = [ [1,2], [ [3,4] ], [ [[5],[6]] ] ]; const flatten = arr => arr.reduce((a, v) => { if (v instanceof Array) { return a.concat(flatten(v)) } else { a.push(v); return a; } }, []) console.log(flatten(a));

Answer 2

 let arr = [[1,2],[[3,4]],[[[5],[6]]]]; const flattenArr = (arr) => arr.reduce((acc, val) => Array.isArray(val) ? acc.concat(flattenArr(val)) : acc.concat(val), []); console.log(flattenArr(arr));

Answer 3

let array = [[2, 4, 6, 8], [10, 12, 14], [16, 18, 20, 22]]

const flatten = array.reduce((a, b) => {
  return a.concat(b)
})

console.log(flatten)