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# Utilities
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Path resolution and routing utility functions for advanced routing scenarios and custom integrations.
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## Capabilities
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### Path Resolution
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Resolves relative paths against base paths, following directory-like navigation semantics.
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```javascript { .api }
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/**
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 * Resolves URIs as though every path is a directory, no files
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 * @param to - Target path (relative or absolute)
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 * @param base - Base path to resolve against
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 * @returns Resolved absolute path
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 */
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function resolve(to: string, base: string): string;
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```
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**Usage Examples:**
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```javascript
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import { resolve } from "@reach/router";
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// Absolute paths pass through unchanged
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resolve("/foo/bar", "/baz/qux"); // => "/foo/bar"
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// Relative paths resolve against base
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resolve("profile", "/users/123"); // => "/users/123/profile"
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// Parent directory navigation
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resolve("../settings", "/users/123/profile"); // => "/users/123/settings"
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resolve("../../admin", "/users/123/profile"); // => "/admin"
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// Query string handling
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resolve("?tab=settings", "/users/123"); // => "/users/123?tab=settings"
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```
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### Parameter Interpolation
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Inserts parameters into path templates with dynamic segments.
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```javascript { .api }
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/**
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 * Interpolates parameters into a path template
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 * @param path - Path template with parameter placeholders
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 * @param params - Object containing parameter values
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 * @returns Path with parameters interpolated
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 */
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function insertParams(path: string, params: Record<string, any>): string;
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```
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**Usage Examples:**
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```javascript
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import { insertParams } from "@reach/router";
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// Basic parameter insertion
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insertParams("/users/:userId", { userId: "123" }); 
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// => "/users/123"
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// Multiple parameters
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insertParams("/users/:userId/posts/:postId", { 
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  userId: "123", 
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  postId: "456" 
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}); 
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// => "/users/123/posts/456"
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// With query parameters
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insertParams("/search/:query", { 
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  query: "react",
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  location: { search: "?type=posts" }
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});
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// => "/search/react?type=posts"
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```
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### Redirect Validation
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Validates that redirect routes have matching dynamic segments.
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```javascript { .api }
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/**
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 * Validates that redirect from/to paths have matching dynamic segments
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 * @param from - Source path pattern
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 * @param to - Target path pattern  
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 * @returns True if redirect is valid, false otherwise
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 */
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function validateRedirect(from: string, to: string): boolean;
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```
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**Usage Examples:**
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```javascript
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import { validateRedirect } from "@reach/router";
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// Valid redirects - matching dynamic segments
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validateRedirect("/old/:id", "/new/:id"); // => true
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validateRedirect("/users/:userId/posts/:postId", "/u/:userId/p/:postId"); // => true
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// Invalid redirects - mismatched segments
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validateRedirect("/old/:id", "/new/:otherId"); // => false
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validateRedirect("/users/:userId", "/posts/:postId"); // => false
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// Static paths
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validateRedirect("/old-path", "/new-path"); // => true
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```
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### Object Comparison
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Performs shallow comparison of two objects for equality.
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```javascript { .api }
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/**
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 * Shallow compares two objects for equality
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 * @param obj1 - First object to compare
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 * @param obj2 - Second object to compare
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 * @returns True if objects have same keys and values, false otherwise  
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 */
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function shallowCompare(obj1: object, obj2: object): boolean;
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```
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**Usage Examples:**
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```javascript
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import { shallowCompare } from "@reach/router";
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// Equal objects
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shallowCompare({ a: 1, b: 2 }, { a: 1, b: 2 }); // => true
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// Different values
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shallowCompare({ a: 1, b: 2 }, { a: 1, b: 3 }); // => false
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// Different keys
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shallowCompare({ a: 1, b: 2 }, { a: 1, c: 2 }); // => false
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// Nested objects (shallow comparison)
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shallowCompare(
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  { a: { nested: true } }, 
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  { a: { nested: true } }
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); // => false (different object references)
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```