擅长:python、mysql、java
<p>枚举是一个typescript概念,在<a href="https://www.typescriptlang.org/docs/handbook/enums.html" rel="nofollow noreferrer">here</a>中有文档记录。编写枚举时,typescript正在创建一个与枚举选项匹配的普通js对象,因此可以使用“in”运算符检查提供的值是否是枚举的成员</p>
<p>类型脚本枚举</p>
<pre class="lang-js prettyprint-override"><code>enum Direction {
Up,
Down,
Left,
Right,
}
</code></pre>
<p>这在javascript中是什么</p>
<pre class="lang-js prettyprint-override"><code>var Direction = {
'0': 'Up',
'1': 'Down',
'2': 'Left',
'3': 'Right',
Up: 0,
Down: 1,
Left: 2,
Right: 3
}
</code></pre>
<p>检查某个值是否是枚举的成员可以使用</p>
<pre class="lang-js prettyprint-override"><code>const foo = "Up";
// Unsafe, but quick and easy.
console.log(foo in Direction); // returns true.
console.log("toString" in Direction); // also returns true.
// Safe.
console.log(Direction.hasOwnProperty(foo)); // returns true.
console.log(Direction.hasOwnProperty(foo)); // returns false.
</code></pre>