JavaScript 展平嵌套数组

Question

I am trying to flatten any length of a nested array into a single array. Why it's showing array rather than array value?

 function flatten(arr) { var res = []; for (var i = 0; i < arr.length; i++) { if (toString.call(arr[i]) === "[object Array]") { res.push(flatten(arr[i])); } else { res.push(arr[i]); } } return res; } console.log(flatten([1, 2, [3, [4, 5, [6]]], 7, 8])); // [1, 2, Array(2), 7, 8]

Answer 1

You are pushing to res the result of flatten , which is an array. Instead Array#concat the result of the inner flatten call to res , and assign the result to res .

Note: to identify an array, you can use Array#isArray .

 function flatten(arr) { var res = []; for (var i = 0; i < arr.length; i++) { if (Array.isArray(arr[i])) { res = res.concat(flatten(arr[i])); } else { res.push(arr[i]); } } return res; } console.log(flatten([1, 2, [3, [4, 5, [6]]], 7, 8])); // [1, 2, Array(2), 7, 8]

Answer 2

You can use concat instead of push and reduce instead of for loop.

 const flatten = data => data.reduce((r, e) => { return r = r.concat(Array.isArray(e) ? flatten(e) : e), r }, []) console.log(flatten([1, 2, [3, [4, 5, [6]]], 7, 8]))

Answer 3

You can use the flat() method on the array as follows.

 function flatten(arr) { return arr.flat(10) //the number in brackets are the depth level } console.log(flatten([1, 2, [3, [4, 5, [6]]], 7, 8]));