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filter_map.html
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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport"
content="width=device-width, initial-scale=1.0">
<title>filter map</title>
</head>
<body>
<h1>filter map</h1>
<p>请你给原生的 Map 添加方法 filterKeys 和 filterValues，可以类似于于数组方法的 filter。它们分别可以对 Map 的键和值进行筛选，它们会返回一个新的 Map， 是对原有的 Map 的筛选结果</p>
<p>例如：</p>
<pre>
const m = new Map([['Jerry', 12], ['Jimmy', 13], ['Tomy', 14]])
m.filterKeys((key) => key.startsWith('J')) // => Map { Jerry => 12, Jimmy => 13 }
m.filterValues((val) => val >= 13) // => Map { Jimmy => 13, Tomy => 14 }
// 原有的 map 保持不变
console.log(m) // => Map { Jerry => 12 , Jimmy => 13, Tomy => 14 }
</pre>
<script>
const m = new Map([['Jerry', 12], ['Jimmy', 13], ['Tomy', 14]])
Map.prototype.filterKeys = function (fn) {
const newMap = new Map();
for (const [key, val] of this) {
if (fn && fn(key)) newMap.set(key, val)
}
return newMap;
}
Map.prototype.filterValues = function (fn) {
const newMap = new Map();
for (const [key, val] of this) {
if (fn && fn(val)) newMap.set(key, val)
}
return newMap;
}
const m1 = m.filterKeys((key) => key.startsWith('J'))
const m2 = m.filterValues((val) => val >= 13)
console.log('m1', m1)
console.log('m2', m2)
</script>
</body>
</html>