Concatination helper, which can merge class names together. Skips over falsey values.

cssConcat.js

function css() {
    var args = [];
    for (var _i = 0; _i < arguments.length; _i++) {
        args[_i] = arguments[_i];
    }
    var classes = [];
    for (var _a = 0, args_1 = args; _a < args_1.length; _a++) {
        var arg = args_1[_a];
        if (arg) {
            if (typeof arg === 'string') {
                classes.push(arg);
            }
            else if ((arg.hasOwnProperty('toString') && typeof (arg.toString) === 'function')) {
                classes.push(arg.toString());
            }
            else {
                // tslint:disable-next-line:no-any
                for (var key in arg) {
                    // tslint:disable-next-line:no-any
                    if (arg[key]) {
                        classes.push(key);
                    }
                }
            }
        }
    }
    return classes.join(' ');
}