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# resolve-pathname
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resolve-pathname provides a pure JavaScript implementation for resolving URL pathnames that is 100% compatible with browser pathname resolution behavior. It resolves pathnames identically to how browsers resolve the pathname of an `<a href>` value, supporting both absolute and relative path resolution, proper handling of '..' and '.' path segments, and maintaining trailing slash behavior.
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## Package Information
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- **Package Name**: resolve-pathname
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- **Package Type**: npm
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- **Language**: JavaScript (ES6 modules with CommonJS build)
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- **Installation**: `npm install resolve-pathname`
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## Core Imports
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```javascript
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// ES6 modules
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import resolvePathname from 'resolve-pathname';
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```
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For CommonJS:
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```javascript
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// CommonJS modules
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var resolvePathname = require('resolve-pathname');
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```
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For UMD (browser):
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```html
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<script src="https://unpkg.com/resolve-pathname"></script>
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<!-- Available as window.resolvePathname -->
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```
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## Basic Usage
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```javascript
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import resolvePathname from 'resolve-pathname';
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// Simply pass the pathname you'd like to resolve. Second
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// argument is the path we're coming from, or the current
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// pathname. When undefined, it defaults to empty string.
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resolvePathname('about', '/company/jobs'); // /company/about
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resolvePathname('../jobs', '/company/team/ceo'); // /company/jobs
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resolvePathname('about'); // about
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resolvePathname('/about'); // /about
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// Index paths (with a trailing slash) are also supported and
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// work the same way as browsers.
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resolvePathname('about', '/company/info/'); // /company/info/about
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// In browsers, it's easy to resolve a URL pathname relative to
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// the current page. Just use window.location! e.g. if
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// window.location.pathname == '/company/team/ceo' then
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resolvePathname('cto', window.location.pathname); // /company/team/cto
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resolvePathname('../jobs', window.location.pathname); // /company/jobs
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```
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## Capabilities
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### Pathname Resolution
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Resolves URL pathnames using the same algorithm as browsers, providing 100% compatibility with browser pathname resolution behavior.
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```javascript { .api }
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/**
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 * Resolve URL pathnames identical to how browsers resolve the pathname of an <a href> value.
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 * 
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 * @param {string} to - The pathname to resolve (can be relative or absolute)
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 * @param {string} [from] - The current pathname to resolve from (optional, defaults to empty string when undefined)
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 * @returns {string} The resolved pathname
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 */
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function resolvePathname(to, from);
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```
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**Parameters:**
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- `to` (string): The pathname you want to resolve. Can be:
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  - Absolute path (starting with '/'): e.g., '/about'
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  - Relative path: e.g., 'about', '../jobs'
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  - Parent directory reference: e.g., '..'
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  - Current directory reference: e.g., '.'
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  - Empty string: returns the from path unchanged
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- `from` (string, optional): The path we're coming from, or the current pathname. When undefined, defaults to empty string
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**Returns:**
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- (string): The resolved pathname
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**Resolution Behavior:**
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- **Absolute paths**: When `to` starts with '/', it's treated as absolute and returned as-is (after normalization)
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- **Relative paths**: Resolved relative to the `from` path, with proper handling of:
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  - `..` segments: Navigate to parent directory
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  - `.` segments: Stay in current directory (removed)
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  - Trailing slashes: Preserved when appropriate
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- **Empty paths**: Empty `to` returns `from` unchanged
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- **Index paths**: Paths ending with '/' are treated as directory paths
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**Usage Examples:**
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```javascript
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// Absolute path resolution
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resolvePathname('/about', '/company/jobs'); // '/about'
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// Relative path resolution
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resolvePathname('about', '/company/jobs'); // '/company/about'
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// Parent directory navigation
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resolvePathname('../jobs', '/company/team/ceo'); // '/company/jobs'
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// Multiple parent directory navigation
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resolvePathname('../../other', '/company/team/ceo'); // '/other'
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// Current directory reference
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resolvePathname('.', '/company/jobs'); // '/company/'
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// Trailing slash handling
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resolvePathname('about', '/company/'); // '/company/about'
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// Undefined from parameter (defaults to empty string)
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resolvePathname('about'); // 'about'
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resolvePathname('/about'); // '/about'
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// Edge cases
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resolvePathname('', '/company/jobs'); // '/company/jobs'
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resolvePathname('../../../../foo', '/a/b'); // '/foo'
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```