_.map(collection, [iteratee=_.identity])
创建一个经过 iteratee 处理的集合中每一个元素的结果数组。 iteratee 会传入3个参数：(value, index|key, collection)。
<!DOCTYPE html>
<html lang="zh">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<meta http-equiv="X-UA-Compatible" content="ie=edge" />
<title>map</title>
</head>
<body>
<script src="https://cdn.bootcss.com/lodash.js/4.17.10/lodash.min.js"></script>
<script type="text/javascript">
function square(n) {
return n * n;
}
console.log(_.map([4, 8], square));
//[16,64]
var users = [{
'user': 'barney'
},
{
'user': 'fred'
}
];
console.log(_.map(users, 'user'));
//['barney','fred']
</script>
</body>
</html>