上代码
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Document</title>
</head>
<body>
<script>
let arr = ['a', 'a', 'a', 'b', 'b', 'b', 'b', 'c', 'c', 'd']
// 变成
obj = {
a: 3,
b: 4,
c: 2,
d: 1,
}
let obj1 = {}
arr.map((item) => {
if (!obj1[item]) {
obj1[item] = 1
} else {
obj1[item]++
}
})
console.log(obj1)
</script>
</body>
</html>