var_dump(json_decode(json_encode(["0"=>"One", "1"=>"Two", "2"=>"Three"])));

array(3) {
    [0]=>
    string(3) "One"
    [1]=>
    string(3) "Two"
    [2]=>
    string(5) "Three"
}

var_dump(json_decode(json_encode(["1"=>"One", "2"=>"Two", "3"=>"Three"])));

object(stdClass)#1 (3) {
    ["1"]=>
    string(3) "One"
    ["2"]=>
    string(3) "Two"
    ["3"]=>
    string(5) "Three"
}

var_dump(json_decode(json_encode(["One", "Two", "Three"])));

array(3) {
    [0]=>
    string(3) "One"
    [1]=>
    string(3) "Two"
    [2]=>
    string(5) "Three"
}