Efficiently Extract Nested URL Parameters with Recursive Logic in JavaScript

Scenario

Extract the value of a target search parameter (e.g., id) from a nested URL within a URL part, using a given search parameter key (e.g., from).

For example, for the URL /main?from=/details?from=/more?id=456, the function getNestedSearchParamValue extracts the nested URL by looking for the search parameter from.

...

const nestedUrl = new URL(urlPart, dummyUrl);

const nestedUrlPart = nestedUrl.searchParams.get(nestedParamKey) ?? "";

...

First, the nested URL /details?from=/more?id=456 is extracted. Since the URL contains another from search parameter, the getNestedSearchParamValue function calls itself, passing the extracted URL /details?from=/more?id=456 as the urlPart, along with the same nestedParamKey (from) and targetParamKey (id).

...

if(nestedUrlPart.includes(nestedParamKey)){
    return getNestedSearchParamValue(nestedUrlPart, nestedParamKey, targetParamKey);
}

...

In the first recursive call, the nestedUrlPart becomes /more?id=456. Because this URL does not contain the search parameter from (the nestedParamKey), it indicates that this is the target URL to search for the id parameter (the targetParamKey). Therefore, extract the value of the search parameter id from this url part.

...

else {
    const targetUrl = new URL(nestedUrlPart, dummyUrl);
    return targetUrl.searchParams.get(targetParamKey);
}

...

Function

const dummyUrl = "http://localhost";

function getNestedSearchParamValue(urlPart: string, nestedParamKey: string, targetParamKey: string): string | null {
    const nestedUrl = new URL(urlPart, dummyUrl);

    const nestedUrlPart = nestedUrl.searchParams.get(nestedParamKey) ?? "";
    if(!nestedUrlPart){
        return null;
    }
    if(nestedUrlPart.includes(nestedParamKey)){
        return getNestedSearchParamValue(nestedUrlPart, nestedParamKey, targetParamKey);
    }
    else {
        const targetUrl = new URL(nestedUrlPart, dummyUrl);
        return targetUrl.searchParams.get(targetParamKey);
    }
}

Usage

const url = "/main?from=/details?from=/more?id=456";

const value = getNestedSearchParamValue(url, "from", "id");
console.log(value);

Output

[LOG]: "456" 

Alternative: use URLSearchParams

With a helper function getUrlPartSearchParams

const queryDelimiter = "?";

function getUrlPartSearchParams(urlPart: string):URLSearchParams | null {
    const [_, ...query] = urlPart.split(queryDelimiter);
    const queryStr = query.join(queryDelimiter);
    return new URLSearchParams(queryStr);
}

Function getNestedSearchParamValue becomes

function getNestedSearchParamValue(urlPart: string, nestedParamKey: string, targetParamKey: string): string | null {
    let searchParams = getUrlPartSearchParams(urlPart);

    const nestedUrlPart = searchParams?.get(nestedParamKey);
    // console.log(nestedUrlPart)
    if(!nestedUrlPart) {
        return null;
    }
    if (nestedUrlPart.includes(nestedParamKey)) {
        return getNestedSearchParamValue(nestedUrlPart, nestedParamKey, targetParamKey);
    } else {
        searchParams = getUrlPartSearchParams(nestedUrlPart);
        return searchParams?.get(targetParamKey) ?? null;
    }
}

Resources

• https://developer.mozilla.org/en-US/docs/Web/API/URL

• https://developer.mozilla.org/en-US/docs/Web/API/URLSearchParams

• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/rest_parameters

• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/split

• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/join

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