button.js

/*
 Add a button to show/hide activity tab.  This button floats on top of the workspace switcher and won't play nicely with the interface when the workspace switcher isn't open.

 Copy and paste this code into the dev console (run /slackdevtools to open the console or set the SLACK_DEVELOPER_MENU environment variable to TRUE so you can right click on elements).

 The code tries to reinsert itself when slack modifies its interface, but if you need to recreate the button, simply open the dev console again and hit the up arrow.
*/

var b;
var thing = $; //no idea why $ isn't defined within handler

function fixSlack() {
    thing('.p-control_strip').style.left = 0
    thing('.p-control_strip').style.width = "64px"

    b = document.createElement('button');
    b.classList.add('c-button-unstyled');
    b.classList.add('p-control_strip__circle_button');
    b.classList.add('p-control_strip__create_button');
    b.style.padding = '5pt';
    b.innerHTML = "<svg data-pe9=\"true\" aria-hidden=\"true\" viewBox=\"0 0 20 20\" class=\"\" style=\"--s: 20px;\"><path fill=\"currentColor\" fill-rule=\"evenodd\" d=\"M4.836 3A1.836 1.836 0 0 0 3 4.836v7.328c0 .9.646 1.647 1.5 1.805V7.836A3.336 3.336 0 0 1 7.836 4.5h6.133A1.837 1.837 0 0 0 12.164 3H4.836ZM1.5 12.164a3.337 3.337 0 0 0 3.015 3.32A3.337 3.337 0 0 0 7.836 18.5h3.968c.73 0 1.43-.29 1.945-.805l3.946-3.946a2.75 2.75 0 0 0 .805-1.945V7.836a3.337 3.337 0 0 0-3.015-3.32A3.337 3.337 0 0 0 12.164 1.5H4.836A3.336 3.336 0 0 0 1.5 4.836v7.328ZM7.836 6A1.836 1.836 0 0 0 6 7.836v7.328C6 16.178 6.822 17 7.836 17H11.5v-4a1.5 1.5 0 0 1 1.5-1.5h4V7.836A1.836 1.836 0 0 0 15.164 6H7.836Zm8.486 7H13v3.322L16.322 13Z\" clip-rule=\"evenodd\"></path></svg>";

    var tabstate = 1;
    b.addEventListener("click", function() {
        if(tabstate) {
            thing('.p-client_workspace_wrapper').style['grid-template-columns'] = "0px auto";
            thing('.p-tab_rail').style.width = "0px";
            tabstate = 0;
        } else {
            thing('.p-client_workspace_wrapper').style['grid-template-columns'] = "64px auto";
            thing('.p-tab_rail').style.width = "64px";        
            tabstate = 1;
        }
    });
    thing('.p-control_strip').prepend(b);
    
    const observer = new MutationObserver(function(mutationList, observer) {        
        for(mut of mutationList) {
            if(mut.type == "childList" && mut.removedNodes) {
                if(!document.contains(b)) {
                    let oldb = b;
                    fixSlack();
                    if(oldb != b) {
                        //successfully created new b
                        observer.disconnect();
                    }
                    return;
                }
            }
        }
    });
    observer.observe(document.body, {childList:true});
}

fixSlack();