反向数组功能在javascript中不起作用

Question

I want to reverse an array without using the built-in methods but the following function is not working:

function reverseArray(arr) {
  let brandNewArray = [];

  for (let i = arr.length - 1; i >= 0; i--) {
    brandNewArray += arr[i];
  }

  return brandNewArray;
}


reverseArray([1,2,3]);

Answer 1

Use push function instead of += .

 function reverseArray(arr) { let brandNewArray = []; for (let i = arr.length - 1; i >= 0; i--) { brandNewArray.push(arr[i]); } return brandNewArray; } console.log(reverseArray([1,2,3])); 

Answer 2

Instead of += you need to push items into it. Using += at first time will assign to the brandNewArray a string, (as [] + 1 will give you "1" ), with value of the last item. Then string concatenation goes and you got 321 as the final value of brandNewArray instead of array.

 function reverseArray(arr) { let brandNewArray = []; for (let i = arr.length - 1; i >= 0; i--) { brandNewArray.push(arr[i]); } return brandNewArray; } console.log(reverseArray([1,2,3])) 

Also you can use more compact version of your code

 const reverseArray = arr => arr.reduce((acc, cur) => (acc.unshift(cur), acc), []); console.log(reverseArray([1,2,3]))