How to pass variable from input from popup.js to inject.js?

Question

JavaScript

popup.html has an input and a button

<input type="text" id="numb" class="no">
<button id="sub" class="subsave">Start</button>

in popup.js I get the value of this input and send inject.js to the site page

var btn = document.getElementById("sub");
btn.addEventListener('click', start);
function start(e) {
       chrome.tabs.executeScript({
            code: "let inp = " + document.getElementById("numb").value,  
            allFrames: true
       }, function(result) {
           chrome.tabs.executeScript({file: "/js/inject.js", allFrames: true}, function(result) {
           });
       });
}

But when run in the console, it gives an error Uncaught TypeError: Cannot read property 'value' of null
What should I do?

Answer 1

Popup plays by the same rules as any other page.
You need to wait for DOMContentLoaded and then bind the events and allow them to work.