An example outlining typescript and path parameter injection to strings.

endpoint-path-typestring.ts

/****************Data model type***************/

interface Endpoint<
T_Path extends string = string,
> {
    path: T_Path
}

// Examples

const getUser: Endpoint<'/api/users'> = {
    path: '/api/users',
}

const getUserById: Endpoint<'/api/users/:user_id'> = {
    path: '/api/users/:user_id'
}

const getProjectsForUserById: Endpoint<'/api/users/:user_id/projects'> = {
    path: '/api/users/:user_id/projects'
}

const getProjectByIdForUserById: Endpoint<'/api/users/:user_id/projects/:project_id'> = {
    path: '/api/users/:user_id/projects/:project_id'
}

/****************Param parsing***************/

type TrimLeadingChar<T extends string, C extends string> = T extends `${C}${infer Rest}` ? Rest : T;
type TrimTrailingChar<T extends string, C extends string> = T extends `${infer Rest}${C}` ? Rest : T;

type ParseUrlParams<T_Path extends string, T_Params extends string[] = []> = T_Path extends `${infer T_PathPart}/${infer T_Rest}`
? T_PathPart extends `:${infer T_ParamName}` 
    ? ParseUrlParams<T_Rest, [...T_Params, T_ParamName]>
    : ParseUrlParams<T_Rest, T_Params> 
: T_Params;

type InferEndpointParams<T_Endpoint extends Endpoint> = T_Endpoint extends Endpoint<infer T_Path>
? ParseUrlParams<`${TrimTrailingChar<TrimLeadingChar<T_Path, '/'>, '/'>}/`>
: never;

const getParamsFromEndpoint = <T_Endpoint extends Endpoint>(endpoint: T_Endpoint): InferEndpointParams<T_Endpoint> => {
    if (endpoint.path.startsWith('/')) {
        return getParamsFromEndpoint({
            ...endpoint,
            path: endpoint.path.substring(1)
        })
    }
    if (endpoint.path.endsWith('/')) {
        return getParamsFromEndpoint({
            ...endpoint,
            path: endpoint.path.substring(0, endpoint.path.length - 1)
        })
    }

    const endpointParams = endpoint.path.split('/').reduce((params: string[], pathPart) => {
        if (pathPart.startsWith(':')) {
            params.push(pathPart.substring(1))
        }
        return params
    }, []) as InferEndpointParams<T_Endpoint>
    return endpointParams;
}

// Examples
let getUserParams: InferEndpointParams<typeof getUser>;
let getUserByIdParams: InferEndpointParams<typeof getUserById>;
let getProjectsForUserByIdParams: InferEndpointParams<typeof getProjectsForUserById>
let getProjectByIdForUserByIdParams: InferEndpointParams<typeof getProjectByIdForUserById>

getUserParams = getParamsFromEndpoint(getUser);
getUserByIdParams = getParamsFromEndpoint(getUserById)
getProjectsForUserByIdParams = getParamsFromEndpoint(getProjectsForUserById)
getProjectByIdForUserByIdParams = getParamsFromEndpoint(getProjectByIdForUserById)

/****************Param Population***************/

type EndpointParams<T_EndpointParams extends string[]> = {
  [Key in T_EndpointParams[number]]: string
} & {}

// Examples
const getUserParamObject: EndpointParams<typeof getUserParams> = {};
const getUserByIdParamObject: EndpointParams<typeof getUserByIdParams> = {
    user_id: '1'
};
const getProjectsForUserByIdParamsObject: EndpointParams<typeof getProjectsForUserByIdParams> = {
    user_id: '1'
};
const getProjectByIdForUserByIdParamsObject: EndpointParams<typeof getProjectByIdForUserByIdParams> = {
    user_id: '1',
    project_id: '2'
};

/****************Url generation***************/

type PopulateUrlParams<T_Path extends string, T_Params extends Record<string, string>, T_Url extends string = ''> = T_Path extends `${infer T_PathPart}/${infer T_Rest}`
? T_PathPart extends `:${infer T_ParamName}` 
    ? PopulateUrlParams<T_Rest, T_Params, `${T_Url}/${T_Params[T_ParamName]}`>
    : PopulateUrlParams<T_Rest, T_Params, `${T_Url}/${T_PathPart}`> 
: T_Url;

type InferEndpointUrl<T_Endpoint extends Endpoint, T_Params extends EndpointParams<InferEndpointParams<T_Endpoint>> = EndpointParams<InferEndpointParams<T_Endpoint>>> = T_Endpoint extends Endpoint<infer T_Path>
? `/${TrimLeadingChar<PopulateUrlParams<`${TrimTrailingChar<TrimLeadingChar<T_Path, '/'>, '/'>}/`, T_Params>, '/'>}`
: never;


function getUrlForEndpoint <T_Endpoint extends Endpoint, T_Params extends EndpointParams<InferEndpointParams<T_Endpoint>>>(...args: T_Params extends Record<string, never> ? [endpoint: T_Endpoint] : [endpoint: T_Endpoint, params: T_Params]): InferEndpointUrl<T_Endpoint> {
    const endpoint = args[0];
    const params = args[1] ?? {};

    let path = endpoint.path;
    if (path.startsWith('/')) {
        path = path.substring(1)
    }
    if (path.endsWith('/')) {
        path = path.substring(0, endpoint.path.length - 1)
    }

    return endpoint.path.split('/').reduce((url: string[], pathPart) => {
        if (pathPart.startsWith(':')) {
            return [...url, params[pathPart.substring(1) as keyof typeof params]]
        }
        return [...url, pathPart]
    }, []).join('/') as InferEndpointUrl<T_Endpoint>
} 

// Examples 

const getUserUrl = getUrlForEndpoint(getUser);
const getUserByIdUrl = getUrlForEndpoint(getUserById, getUserByIdParamObject);
const getProjectsForUserByIdUrl = getUrlForEndpoint(getProjectsForUserById, getProjectsForUserByIdParamsObject);
const getProjectByIdForUserByIdUrl = getUrlForEndpoint(getProjectByIdForUserById, getProjectByIdForUserByIdParamsObject);

/****************Custom Properties***************/

interface Endpoint {
    meta: {
        Component: true
    }
}

const home: Endpoint<'/'> = {
    path: '/',
    meta: {
        Component: true
    }
}

const homeUrl = getUrlForEndpoint(home)

const userProfile: Endpoint<'/users/:user_id'> = {
    path: '/users/:user_id',
    meta: {
        Component: true
    }
}
const userPorfileUrl = getUrlForEndpoint(userProfile, {
    user_id: '1'
})