当需要验证数据时，类特别有用。在本例中，Box 类不应该能够超过滑块允许的最大值继续放大，但事实确实如此。
我们可以通过用Getter 和Setter（也称为访问器）替换width 和height 来修复此问题。首先，将它们转换为私有属性
应用
class Box {
#width = $state(0);
#height = $state(0);
area = $derived(this.#width * this.#height);
constructor(width, height) {
this.#width = width;
this.#height = height;
}
// ...
}然后，创建一些 Getter 和 Setter
应用
class Box {
// ...
get width() {
return this.#width;
}
get height() {
return this.#height;
}
set width(value) {
this.#width = value;
}
set height(value) {
this.#height = value;
}
embiggen(amount) {
this.width += amount;
this.height += amount;
}
}最后，将验证添加到 Setter 中
应用
set width(value) {
this.#width = Math.max(0, Math.min(MAX_SIZE, value));
}
set height(value) {
this.#height = Math.max(0, Math.min(MAX_SIZE, value));
}现在，无论通过范围输入上的bind:value 还是embiggen 方法，都不可能将框大小增加到安全限制以上，无论你按下按钮的力度有多大。
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
<script>
const MAX_SIZE = 200;
class Box {width = $state(0);
height = $state(0);
area = $derived(this.width * this.height);
constructor(width, height) {this.width = width;
this.height = height;
}
embiggen(amount) {this.width += amount;
this.height += amount;
}
}
const box = new Box(100, 100);
</script>
<label>
<input type="range" bind:value={box.width} min={0} max={MAX_SIZE} /> {box.width}</label>
<label>
<input type="range" bind:value={box.height} min={0} max={MAX_SIZE} /> {box.height}</label>
<button onclick={() => box.embiggen(10)}>embiggen</button><hr>
<div
class="box"
style:width="{box.width}px" style:height="{box.height}px">
{box.area}</div>
<style>
label {display: flex;
align-items: center;
}
hr {margin: 1em 0;
border: none;
border-bottom: 1px solid #888;
}
.box {background: radial-gradient(at 25% 25%, hsl(15 100 60), hsl(15 100 50)) ;
border-radius: 2px;
filter: drop-shadow(0 0 10px hsl(15 100 50 / 0.3));
display: flex;
align-items: center;
justify-content: center;
overflow: hidden;
}
</style>