# JS Filter

轻量、易读、可解析、可执行的类 SQL 过滤语法，用于 JavaScript 数组过滤。

## 语法特性

- **WHERE**: 条件过滤
- **ORDER BY**: 排序
- **LIMIT**: 限制结果数量
- **操作符**: `=`, `!=`, `>`, `<`, `>=`, `<=`, `IN`, `CONTAINS`, `LIKE`, `NOT LIKE`, `IS NULL`, `IS NOT NULL`
- **逻辑**: `AND`, `OR`

## 语法示例

```javascript
// 基础过滤
filter(users, "WHERE metadata.type = 'user'");

// 多条件
filter(users, "WHERE metadata.tags CONTAINS 'premium' AND metadata.region = 'beijing'");

// 排序
filter(users, "WHERE metadata.type = 'user' ORDER BY metadata.created_at DESC");

// 限制数量
filter(users, "WHERE metadata.type = 'user' ORDER BY metadata.created_at DESC LIMIT 10");

// IN 操作
filter(users, "WHERE metadata.region IN ['beijing', 'shanghai']");

// LIKE 操作 (支持 % 匹配任意字符，_ 匹配单个字符)
filter(products, "WHERE name LIKE '%Apple%'");
filter(products, "WHERE name LIKE 'Apple%'");
filter(products, "WHERE name LIKE '%Phone'");

// NOT LIKE 操作 (排除匹配模式的项)
filter(products, "WHERE name NOT LIKE '%Apple%'");

// IS NULL 操作 (匹配 null 或 undefined 的值)
filter(users, "WHERE email IS NULL");

// IS NOT NULL 操作 (匹配非 null 且非 undefined 的值)
filter(users, "WHERE email IS NOT NULL");
```

## 使用方法

```javascript
import { filter } from '@kevisual/js-filter';

const users = [
  {
    metadata: {
      tags: ['premium', 'active'],
      type: 'user',
      region: 'beijing',
      created_at: '2024-03-15T10:00:00Z',
    },
  },
  {
    metadata: {
      tags: ['free'],
      type: 'admin',
      region: 'shanghai',
      created_at: '2024-01-10T09:00:00Z',
    },
  },
  {
    metadata: {
      tags: ['enterprise', 'premium'],
      type: 'user',
      region: 'guangzhou',
      created_at: '2024-04-05T12:00:00Z',
    },
  },
];

// 查找 premium 用户
const premiumUsers = filter(users, "WHERE metadata.tags CONTAINS 'premium'");

// 查找北京的用户，按创建时间倒序
const beijingUsers = filter(users, "WHERE metadata.region = 'beijing' ORDER BY metadata.created_at DESC");
```

## 新增操作符说明

### NOT LIKE
排除匹配指定模式的数据项。

```javascript
// 查找不包含 "Apple" 的产品
const nonAppleProducts = filter(products, "WHERE name NOT LIKE '%Apple%'");
```

### IS NULL / IS NOT NULL
检查字段值是否为 `null` 或 `undefined`。

```javascript
const usersWithNullEmail = [
  { name: 'Alice', email: 'alice@example.com', age: 25 },
  { name: 'Bob', email: null, age: 30 },
  { name: 'Charlie', email: undefined, age: 35 },
];

// 查找 email 为 null 或 undefined 的用户
const usersWithoutEmail = filter(usersWithNullEmail, "WHERE email IS NULL");

// 查找 email 不为 null 且不为 undefined 的用户  
const usersWithEmail = filter(usersWithNullEmail, "WHERE email IS NOT NULL");
```

**注意**: `IS NULL` 和 `IS NOT NULL` 会同时检查 JavaScript 的 `null` 和 `undefined` 值。