英文:
Filtering array of objects in svelte typescript
问题
我想检查特定用户名是否在用户对象数组中。
我正在使用FastAPI获取选民列表。用户具有类似{"username": "mickey"}的用户名值。我将当前用户存储在$username中。
<script>
let question = {answers:[], voter:[], content: ''}
function get_question() {
fastapi("get", "/api/question/detail/" + question_id, {}, (json) => {
question = json
}}
</script>
{#if question.voter.forEach(v => v.username).includes($username) }
然而，question.voter.username.forEach(v => v.username) 一直返回未定义。我有点困惑于Python和JavaScript的性质。
或者我的方法有问题吗？我应该创建另一个Fast API调用吗？
英文:
I want to check whether a certain username is in the array of user objects.
I am fetching voter list with fastapi. A user has username value like {"username": "mickey"}. I am storing the current user with persistent_storage as $username.
<script>
let question = {answers:[], voter:[], content: ''}
function get_question() {
fastapi("get", "/api/question/detail/" + question_id, {}, (json) => {
question = json
})}
</script>
{#if question.voter.forEach(v => v.username).includes($username) }
However, question.voter.username.forEach(v => v.username) keeps returning undefined.
I am kinda confused between the nature of python and javascript.
Or is my approach wrong? Should I create another fast API call?
答案1
得分: 1
假设 $username 包含一个字符串值，可以进行如下检查：
{#if question.voter.some(v => v.username === $username)}
另一种可能的方式是：
{#if question.voter.map(v => v.username).includes($username)}
但我认为使用 .some() 更加高效，因为它只迭代数组一次并在找到结果后立即停止。
请注意，您在评论中提到的当前解决方案使用 String.prototype.includes 是容易出错的，因为它将匹配包含当前用户名的更长用户名。例如，当有一个用户对象 {username: 'foobar'} 和 $username = 'foo' 时，这将匹配，即使没有 {username: foo}。可以调整为：
{#if question.voter.filter(v => v.username === $username).length == 1}
但与此相比，这不是首选选项。
英文:
Assuming $username holds a string value the check could be
{#if question.voter.some(v => v.username === $username)}
Also possible would be
{#if question.voter.map(v => v.username).includes($username)}
but I think .some() is besides being shorter also more efficient because it only iterates the array once and stops as soon as a result is found
Notice that your current solution mentioned in the comments using String.prototype.includes
{#if question.voter.filter(v => v.username.includes($username)).length == 1}
is error prone because this will match longer usernames containing the current username. Like when there's a user object {username: 'foobar'} and $username = 'foo' this will match when there's no {username: foo}. Could be adjusted to
{#if question.voter.filter(v => v.username === $username).length == 1}
but compared that's not the preferred option
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