As you can see in the URL, you pass "${encodeURIComponent...}" as a string, not as evaluated value. Your code is probably something like:

    url = 'https://friendbot(...)?addr=${encodeURIComponent...}';

but should be like:

    url = 'https://friendbot(...)?addr=' + encodeURIComponent...;
    // or as a template string
    url = `https://friendbot(...)?addr=${encodeURIComponent...}`;

...and since the public keys do not contain special characters, it's not neccessary to escape it. 

    url = 'https://friendbot(...)?addr=' + pair.publicKey();