多个数组合并为一个数组

const merge1 = arr => { // 合并多个数组
            const result = []
            for (let i = 0; i < arr.length; i++) {
              for (let j = 0; j < arr[i].length; j++) {
                result.push(arr[i][j])
              }
            }
            return result
          }

const merge2 = arr => {
const result = [];
for (let i = 0; i < arr.length; i++) {
result = result.concat(arr[i]);
}
return result;
}

const merge3 = arr => { return Array.prototype.concat.apply([], arr); }

function merge4 (arr) { return [].concat.apply([],arr); }

function merge5(arr) { return [].concat(...arr) }

function merge6(arr) {
arr = Array.prototype.concat.apply([], arr);
return arr.some(Array.isArray) ? merge6(arr) : arr;
}

function merge7 (arr) { 
var isArray = Object.prototype.toString.call(arr) === '[object Array]'; 
  if (isArray && arr.length > 0) { 
  var head = arr[0]; var tail = arr.slice(1); 
  return merge7(head).concat(merge7(tail)); 
 } else { 
  return [].concat(arr);
 } 
}

转载至https://www.w3cplus.com/javascript/merge-flatten-an-array-of-arrays-in-javascript.html