长度12的数组，要求对数据分为3组，每组数据对应位置的数字为前几位的和，并返回12位数组

例如[1,2,3,4,5,6,7,8,9,10,11,12]要求返回[1,3,6,10,5,11,18,26,9,19,30,42]

var arr = [1,2,3,4,5,6,7,8,9,10,11,12];
function add(arr1,newarr1) {
    for( var  i  = 0 ; i < arr1.length ; i++ ){
        var num = 0;
        for( var j  = 0 ; j <= i ; j ++){
            num+=arr1[j]
        }
        newarr1.push(num);
    }
}
function AddNum(arr) {
    var newarr1 = [];
    for(var i  =  0 ; i < arr.length ; i ++ ){
        if(i%4==0){
            add(arr.slice(i,i+4),newarr1)
        }
    }
    return newarr1;
}
console.log('=================');
console.log(AddNum(arr))