Fix errors in a Javascript based Google Chrome extension

I am working on an Chrome browser extension and have been unable to resolve the following errors.

1
Unchecked runtime.lastError: Cannot access contents of url "chrome-search://local-ntp/local-ntp.html". Extension manifest must request permission to access this host.
Context
popup.html

2
Error handling response: TypeError: Cannot read property '0' of undefined
$('#search').val(selection[0]);
Context
popup.html

3
Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user's experience. For more help, check https://xhr.spec.whatwg.org/.

4
Refused to load the script 'https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/js/bootstrap.min.js' because it violates the following Content Security Policy directive: "script-src 'self' blob: filesystem: chrome-extension-resource:". Note that 'script-src-elem' was not explicitly set, so 'script-src' is used as a fallback.
Context
popup.html