As The Code Do:

arr.join(',').split(','); 

创建一个新数组，遍历当前数组，判断每一项的length属性，如果不大于1就放到数组里面，如果大于1就split('')之后在concat到新数组里面。之后再返回新数组就行了。

const arr = ["0", "1", "2", "3,4,5,6", "7,8", "9,10"];
const arr2 = [];

arr.forEach(v => Array.prototype.push.apply(arr2, v.split(',')));

console.log(arr2);

var a = [];
var oldarr = ["0", "1", "2", "3,4,5,6", "7,8", "9,10"];
oldarr.forEach(function(val){
    a = a.concat(val.split(','));
})

// ["0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "10"]
console.log(a);

let arr = ["0", "1", "2", "3,4,5,6", "7,8", "9,10"];
console.log( arr.join().split(/,|''/) )

https://jsfiddle.net/1yqzea2f/

另一种参考

arr.toString().split(',')