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# Presence Checking
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Functions for checking value existence, truthiness, and basic state validation.
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## Capabilities
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### Empty Check
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Checks if the given value is empty (works with objects, arrays, and strings).
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```javascript { .api }
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/**
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 * Checks if the given value is empty
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 * @param value - Value to check (array, object, or string)
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 * @returns True if value is empty
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 * Interfaces: not, all, any
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 */
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function empty(value: any): boolean;
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```
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**Usage Example:**
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```javascript
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is.empty({});              // true
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is.empty([]);              // true
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is.empty('');              // true
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is.not.empty(['foo']);     // true
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is.all.empty('', {}, ['foo']); // false
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is.any.empty([], 42);      // true
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```
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### Existy Check
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Checks if the given value is existy (not null or undefined).
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```javascript { .api }
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/**
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 * Checks if the given value is existy (not null or undefined)
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 * @param value - Value to check
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 * @returns True if value is not null or undefined
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 * Interfaces: not, all, any
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 */
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function existy(value: any): boolean;
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```
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**Usage Example:**
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```javascript
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is.existy({});             // true
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is.existy(null);           // false
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is.not.existy(undefined);  // true
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is.all.existy(null, ['foo']); // false
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is.any.existy(undefined, 42); // true
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```
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### Falsy Check
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Checks if the given value is falsy.
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```javascript { .api }
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/**
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 * Checks if the given value is falsy
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 * @param value - Value to check
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 * @returns True if value is falsy
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 * Interfaces: not, all, any
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 */
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function falsy(value: any): boolean;
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```
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**Usage Example:**
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```javascript
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is.falsy(false);           // true
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is.falsy(null);            // true
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is.not.falsy(true);        // true
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is.all.falsy(null, false); // true
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is.any.falsy(undefined, true); // true
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```
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### Truthy Check
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Checks if the given value is truthy (existy and not false).
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```javascript { .api }
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/**
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 * Checks if the given value is truthy
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 * @param value - Value to check
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 * @returns True if value is truthy
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 * Interfaces: not, all, any
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 */
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function truthy(value: any): boolean;
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```
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**Usage Example:**
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```javascript
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is.truthy(true);           // true
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is.truthy(null);           // false
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is.not.truthy(false);      // true
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is.all.truthy(null, true); // false
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is.any.truthy(undefined, true); // true
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```
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### Space Check
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Checks if the given value is a whitespace character.
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```javascript { .api }
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/**
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 * Checks if the given value is space
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 * @param value - Value to check
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 * @returns True if value is whitespace character
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 * Interfaces: not, all, any
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 */
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function space(value: any): boolean;
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```
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**Usage Example:**
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```javascript
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is.space(' ');             // true
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is.space('foo');           // false
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is.not.space(true);        // true
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is.all.space(' ', 'foo');  // false
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is.any.space(' ', true);   // true
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```