With chrome.storage, how to save a string into local storage and then test for existence?

Question

I am writing a chrome extension where I want to save a string (an URL) into local stage and later test for existence.

For example:

function getURL(e) {
  let domain = e.url;

  //if domain does not exist in local storage, save domain into local storage
}

I looked the tutorial on both chrome.storage.local.get() and set(), but I still can not figure an easy way to do this.

Answer 1

save it in an array and then test it.

function getURL(e) {
  let domain = e.url;

  //if domain does not exist in local storage, save domain into local storage

  // get the saved `urls`
  chrome.storage.local.get("urls", i => {
    // urls might not saved before 
    let urls = i.urls || []
    // test if exists
    if (!urls.includes(domain)) {
      urls.push(domain)
      //save it into store
      chrome.storage.local.set({urls})
    }
  })
}