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TS2345: Argument of type 'number | undefined' is not assignable to parameter of type 'number'

I am trying to create a chrome extension in typescript.

I have the following code, where I try to send a message to contentscript from the background script.

// background script 
chrome.tabs.query({active: true, currentWindow: true}, function(tabs){
   chrome.tabs.sendMessage(tabs[0].id, {action: "open_dialog_box"}, function(response) {
      console.log(response);
but typescript is giving the following error
ERROR in /Users/shobi/Projects/Chrome Extensions/src/js/background.ts(8,37)
      TS2345: Argument of type 'number | undefined' is not assignable to parameter of type 'number'.
  Type 'undefined' is not assignable to type 'number'.
I tried converting the id to an integer using parseInt(), but still its not preventing the error.
                .id is possibly undefined. Use a non-null assertion like tabs[0].id! or better yet, check in your code to make sure it isn't undefined.
– Aaron Beall
                Oct 16, 2018 at 15:08
Chrome's tab .id is possibly undefined (because it's defined as optional in the type definitions), which means when using strictNullChecks you have to either use a non-null assertion:
tabs[0].id!
Or write code to ensure that id is not null:
if (tabs[0].id) { // send message
I'm guessing, but maybe typescript thinks that your tabs array could be empty (and thus not have an item at index [0]) - which is why it's type is inferred as number or undefined?
If this is the case, you should check that tabs[0] exists before trying to access the id property on it.
                Even I think Its a problem with typescripts inference, because i found the solution just now. :)
– Shobi
                Oct 16, 2018 at 15:04
        
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