Javascript - onload event

Question

I am having a problem with onload event when I am opening new tabs without switching to them.

I am trying to write a user script for Chrome that adds "Copy" buttons after pre tags. It works fine when the page I am trying to load is on focus but when I open a new tab in the background, it isn't working.

Is this behaviour expected?

Here's my code:

// ==UserScript==
// @author       Vamsi Krishna | vamsi_ism@outlook.com
// @description  Adds a copy button after 'pre' tags.
// @grant        none
// @homepage     https://github.com/krikx/CopyCode
// @match        *://*/*
// @name         CopyCode
// @version      0.1
// ==/UserScript==

var css = "/* google fonts */ @import url(https://fonts.googleapis.com/css?family=Open+Sans); .kxbt { border-radius: 4px; cursor: pointer; display: inline-block; font-family: 'Open Sans', 'sans-serif'; font-size: 15px; margin-bottom: 5px; padding: 5px; padding-top: 3px; transition: .2s; } .blue { color: #55acee; border: 1px #55acee solid; } .blue:hover { background-color: #55acee; color: #fff; } .green { color: #2ecc71; border: 1px #2ecc71 solid; } .green:hover { color: #fff; background-color: #2ecc71; } .red { color: #e74c3c; border: 1px #e74c3c solid; } .red:hover { color: #fff; background-color: #e74c3c; } /* green and red are almost never used as timeout is too fast to observe any noticible difference */";
var style = document.createElement('style');
style.innerHTML = css;
document.getElementsByTagName('head')[0].appendChild(style);

function Init(){
    var blocks = document.getElementsByTagName('pre');

    for (var id = 0; id < blocks.length; id++){
        var btn = document.createElement('div');
        btn.innerText = 'Copy';
        btn.setAttribute('class', 'kxbt blue');

        InsertAfter(blocks[id], btn);
    }
}

function InsertAfter(refNode, newNode){
    refNode.parentNode.insertBefore(newNode, refNode.nextSibling);
    WireClick(newNode, refNode); // add the click funtionality
}

function WireClick(btn, block){
    btn.addEventListener('click', function(){
        Copy(btn, block);
    });
}

function Copy(btn, block){
    var range = document.createRange();
    range.selectNode(block);

    var sel = getSelection();
    sel.removeAllRanges(); // TODO | removing selection without backup
    sel.addRange(range);

    var success = document.execCommand('copy');
    sel.removeAllRanges(); // possible TODO
    var msg = success ? 'Copied!' : 'Error!';
    var tcls = success ? 'kxbt green' : 'kxbt red';

    btn.innerText = msg;
    btn.setAttribute('class', tcls);
    setTimeout( // revert back to blue in 256ms
        function(btn){
            btn.innerText = 'Copy';
            btn.setAttribute('class', 'kxbt blue');
        },
        256, btn
    )
}

function main(){
    var body = document.getElementsByTagName('body')[0];

    // do not inject twice
    if (body.hasAttribute('data-kxbt-inited')){
        return;
    }

    body.setAttribute('data-kxbt-inited', true);
    Init();
}

// wait until ready
window.addEventListener('load', main);

Answer 1

Adblock Plus probably was the cause of issue.
It is working properly after disabling and re-enabling ABP.

---

As I still don't know the cause of issue or why (apparently) disabling/re-enabling ABP solved the issue, it'd be great if anyone can help.