Push dec repeatedly to an array according to the key dec of an object in the array

Strikethrough format ```
//Push dec repeatedly to an array according to dec
let a = [
{name: '1', dec: 1 },
{name: '2', dec: 2 },
{name: ' 3', dec: 3 },
{name: '4', dec: 3 },
{name: '5', dec: 3 },
{name: '6', dec: 2 },
]

let arr = [];
let arr2 = []; // 最后需要的数据

a.forEach(item => {
    if (!arr.includes(item.dec)) {
        arr.push(item.dec)
        arr2.push([]);
    }
})

a.forEach(item => {
    let indexs = arr.indexOf(item.dec);
    arr2[indexs].push(item);
})

console.log(arr, arr2)