权限没有,则隐藏 function forum_list_access_filter($forumlist, $gid, $allow = 'allowread') { global $grouplist; if (empty($forumlist)) return array(); if (1 == $gid) return $forumlist; $forumlist_filter = $forumlist; $group = $grouplist[$gid]; foreach ($forumlist_filter as $fid => $forum) { if (empty($forum['accesson']) && empty($group[$allow]) || !empty($forum['accesson']) && empty($forum['accesslist'][$gid][$allow])) { unset($forumlist_filter[$fid]); } unset($forumlist_filter[$fid]['accesslist']); } return $forumlist_filter; } function forum_filter_moduid($moduids) { $moduids = trim($moduids); if (empty($moduids)) return ''; $arr = explode(',', $moduids); $r = array(); foreach ($arr as $_uid) { $_uid = intval($_uid); $_user = user_read($_uid); if (empty($_user)) continue; if ($_user['gid'] > 4) continue; $r[] = $_uid; } return implode(',', $r); } function forum_safe_info($forum) { //unset($forum['moduids']); return $forum; } function forum_filter($forumlist) { foreach ($forumlist as &$val) { unset($val['brief'], $val['announcement'], $val['seo_title'], $val['seo_keywords'], $val['create_date_fmt'], $val['icon_url'], $val['modlist']); } return $forumlist; } function forum_format_url($forum) { global $conf; if (0 == $forum['category']) { // 列表URL $url = url('list-' . $forum['fid'], '', FALSE); } elseif (1 == $forum['category']) { // 频道 $url = url('category-' . $forum['fid'], '', FALSE); } elseif (2 == $forum['category']) { // 单页 $url = url('read-' . trim($forum['brief']), '', FALSE); } if ($conf['url_rewrite_on'] > 1 && $forum['well_alias']) { if (0 == $forum['category'] || 1 == $forum['category']) { $url = url($forum['well_alias'], '', FALSE); } elseif (2 == $forum['category']) { // 单页 $url = ($forum['threads'] && $forum['brief']) ? url($forum['well_alias'] . '-' . trim($forum['brief']), '', FALSE) : url($forum['well_alias'], '', FALSE); } } return $url; } function well_forum_alias() { $forumlist = forum_list_cache(); if (empty($forumlist)) return ''; $key = 'forum-alias'; static $cache = array(); if (isset($cache[$key])) return $cache[$key]; $cache[$key] = array(); foreach ($forumlist as $val) { if ($val['well_alias']) $cache[$key][$val['fid']] = $val['well_alias']; } return array_flip($cache[$key]); } function well_forum_alias_cache() { global $conf; $key = 'forum-alias-cache'; static $cache = array(); // 用静态变量只能在当前 request 生命周期缓存,跨进程需要再加一层缓存:redis/memcached/xcache/apc if (isset($cache[$key])) return $cache[$key]; if ('mysql' == $conf['cache']['type']) { $arr = well_forum_alias(); } else { $arr = cache_get($key); if (NULL === $arr) { $arr = well_forum_alias(); !empty($arr) AND cache_set($key, $arr); } } $cache[$key] = empty($arr) ? '' : $arr; return $cache[$key]; } ?>error handling - How to catch array index out of bound in JavaScript? - Stack Overflow
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error handling - How to catch array index out of bound in JavaScript? - Stack Overflow

programmeradmin8浏览0评论

I want to catch an error when access outside of array's bounds happens but it doesn't seem to throw an error.

let arr = [2,4,5];
let test = arr[3];
console.log(test);

I know that I can test for undefined and throw an error

if (arr[3] === undefined) throw new Error();

but how e I can't just do try and catch it like the following.

let arr = [2,4,5];
try {
      let tmp = arr[3];
    } catch(e) {
      lastIndex = findLastIndex(arr, high / 2, high);
      break;
    }

I want to catch an error when access outside of array's bounds happens but it doesn't seem to throw an error.

let arr = [2,4,5];
let test = arr[3];
console.log(test);

I know that I can test for undefined and throw an error

if (arr[3] === undefined) throw new Error();

but how e I can't just do try and catch it like the following.

let arr = [2,4,5];
try {
      let tmp = arr[3];
    } catch(e) {
      lastIndex = findLastIndex(arr, high / 2, high);
      break;
    }
Share Improve this question asked Jul 4, 2019 at 21:46 CodeCrackCodeCrack 5,37311 gold badges47 silver badges75 bronze badges 3
  • 1 Accessing an undefined property in JavaScript does not cause a runtime error. It's just the way the language works. – Pointy Commented Jul 4, 2019 at 21:50
  • Yes, JS doesn't throw an error when accessing a non-existing property. If you want to handle it, do it anticipatory: if (i < arr.length) tmp = arr[i] else …. – Bergi Commented Jul 4, 2019 at 21:55
  • @Bergi that's a good solution – CodeCrack Commented Jul 6, 2019 at 21:11
Add a ment  | 

1 Answer 1

Reset to default 8

As you can see, accessing a non-existent array index does not throw an error - the value "accessed" will simply be undefined. Ordinary objects work the same way:

const obj = {};
// No error:
const val = obj.foo;

console.log(val);

But errors generally should not be used for control flow - errors should handle exceptional cases. For what you're doing, I'd use if/else instead, eg

const arr = [0, 1, 2];
if (4 in arr) {
  const val = arr[4];
  // ...
} else {
  console.log('4 is not in the arr');
}

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