Debug doesn't work in IE11

args[0].replace(/%[a-zA-Z%]/g, match => {
        if (match === '%%') {
            return;
        }
        index++;
        if (match === '%c') {
            // We only are interested in the *last* %c
            // (the user may have provided their own)
            lastC = index;
        }
    });

The issue from bundle.js pointed to first line of this part of code

[Diokuz]

Even React supports es5 https://reactjs.org/docs/react-dom.html#browser-support

but not debug)

[Qix-]

Yes, please search before opening issues. Debug 4 doesn’t work in ie11 without transpilation, such as with Babel.