YouTube Music userscript: moves the Save to library button in the player bar

manifest.json

{
	"manifest_version": 2,
	"content_scripts": [
		{
			"exclude_globs": [],
			"include_globs": [
				"*"
			],
			"js": [
				"YoutubeMusicScript.user.js"
			],
			"matches": [
				"https://music.youtube.com/*"
			],
			"run_at": "document_end"
		}
	],
	"converted_from_user_script": true,
	"description": "Youtube Music button 'Save to library' moved in player bar",
	"name": "Youtube Music save to library in player",
	"author": "Nicolas Mollet",
	"version": "1.01"
}

YoutubeMusicScript.user.js

// ==UserScript==
// @name           YouTubeMusicScript
// @description    YouTubeMusicScript
// @include        http://music.youtube.com/*
// @autho          Nicolas Mollet
// @version        1.0
// ==/UserScript==


// Observe play-button clicks.
const play_buttons = document.querySelectorAll('#play-button');
play_buttons.forEach(play_button=>{
    play_button.onclick = function () {
      moveSaveLibraryToPlayerBar();
    }
});

// Configure Observer of mutations to catch song change.
const targetNode = document.body;
const config = { childList: true, subtree: true };
const checkMutations = function(mutationsList, observer) {
    for(let mutation of mutationsList) {
        if (mutation.type === 'childList') {
            // Detect song has changed
            if( mutation.target.className === 'title style-scope ytmusic-player-bar'){
                moveSaveLibraryToPlayerBar();
            }
            // Detect player bad appeared.
            if( mutation.target.className === 'menu style-scope ytmusic-player-bar'){
                moveSaveLibraryToPlayerBar();
            }


        }
    }
};
const observer = new MutationObserver(checkMutations);
observer.observe(targetNode, config);

// Function that moves the "Library button" to the player bar.
const moveSaveLibraryToPlayerBar = function() {
    const playerbar_middle_control_buttons = document.querySelector('.middle-controls-buttons.ytmusic-player-bar');

    if(playerbar_middle_control_buttons.lastElementChild.textContent.includes('Remove from library') || playerbar_middle_control_buttons.lastElementChild.textContent.includes('Save to library')){
        playerbar_middle_control_buttons.removeChild(playerbar_middle_control_buttons.lastElementChild);
    }

    // Browse all buttons.
    const buttons = document.querySelectorAll('ytmusic-player-bar .ytmusic-menu-renderer button');
    buttons.forEach(el=>{
        // Open the song menu.
        el.click();
        setTimeout(() => {

                // Find all menu items.
                const menu_items = document.querySelectorAll('ytmusic-toggle-menu-service-item-renderer');
                menu_items.forEach( menu_item=> {
                    // Find all menu items elements.
                    const menu_item_elements = menu_item.querySelectorAll('yt-formatted-string');
                    menu_item_elements.forEach(menu_item_element=>{

                    if(menu_item_element.textContent === 'Remove from library' || menu_item_element.textContent === 'Save to library'){
                        playerbar_middle_control_buttons.append(menu_item_element.parentNode);
                    }
                    });
                })
        }, 300);
        // Close the song menu.
        el.click();
    })
}

// On load actions.
window.addEventListener ("load", function()
{
    setTimeout(() => {
        moveSaveLibraryToPlayerBar()
    }, 300);
})