Question

给出一些冻结的对象：

const obj = Object.freeze({a: 1, b:2});

它的类型为Readonly<{a:number, b:number}>，是否有任何方法可以定义它，使其类型为Readonly<{a:1, b:2}>，而无需进行强制转换？

我想要这样做的原因是，我想使用值类型来缩小另一个函数的输入范围，例如：function foo(input: 1 | 2)

Answer 1

function l<T extends number>(p: T ): T { 
   return p;
}
const c = { a: l(1), b: l(2) };
// const fc: Readonly<{ a: 1; b: 2; }>
const fc = Object.freeze(c);

或

function lc<T extends number>(p: { [k: string]: T }) : { [k: string]: T } { 
    return p;
}
// const t1: { [k: string]: 1 | 2 | 3; }
const t1 = lc({ a: 1, b: 2, c: 3 });

Answer 2

如果要保持值的不变性，只需使用冻结的装饰器定义Readonly类即可。

export function frozen(target: Function): void {
    Object.freeze(target);
    Object.freeze(target.prototype);
}

Answer 3

在即将发布的TypeScript（3.4）版本中，您可以执行以下操作：

<?php

$con=mysql_connect('localhost', '1093913', 'tanim1996');
$db=mysql_select_db('1093913');

if(isset($_POST['button'])){    //trigger button click
    $numRows = 0;
    if(!empty($_POST['search'])) {
        $search = mysql_real_escape_string($_POST['search']);
        $query = mysql_query("select * from iconic19 where student_id like '%{$search}%' || name like '%{$search}%' || phone like '%{$search}%' || blood like '%{$search}%' || district like '%{$search}%' ");
        $numRows = (int)mysql_num_rows($query);
    }

    if ($numRows > 0) {                 
        while ($row = mysql_fetch_array($query)) {

            echo "<tbody>";
            echo "<tr>";
            echo "<td data-label='Student ID'>".$row['student_id']."</td>";
            echo "<td data-label='Name' style='font-weight:bold;' >".$row['name']."</td>";
            echo "<td data-label='Mobile No'>"."<a href='tel:".$row['phone']."'>".$row['phone']."</a>"."</td>";
            echo "<td data-label='Blood' style='color:red; font-weight:bold;' >".$row['blood']."</td>";
            echo "<td data-label='Email'>"."<a href='mailto:".$row['email']."'>".$row['email']."</a>"."</td>";
            echo "<td data-label='District'>".$row['district']."</td>";
            echo "</tr>";
            echo "</tbody>";

        }
    } else {
        echo "<div class='error-text'>No results</div><br><br>";
    }
} else {                          //while not in use of search  returns all the values
    $query = mysql_query("select * from iconic19");

    while ($row = mysql_fetch_array($query)) {



    }
}

mysql_close();

?>

对象冻结文字对象类型

3 个答案: