1// Copyright (C) 2023 The Android Open Source Project 2// 3// Licensed under the Apache License, Version 2.0 (the "License"); 4// you may not use this file except in compliance with the License. 5// You may obtain a copy of the License at 6// 7// http://www.apache.org/licenses/LICENSE-2.0 8// 9// Unless required by applicable law or agreed to in writing, software 10// distributed under the License is distributed on an "AS IS" BASIS, 11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12// See the License for the specific language governing permissions and 13// limitations under the License. 14 15// It's common to want to have a class depending on a boolean flag, in which 16// case we use `flag && className` which evaluates to either false or a string, 17// which is why false is included in definition of ArgType. 18type ArgType = string | false | undefined; 19 20// Join class names together into valid HTML class attributes 21// Falsy elements are ignored 22// If all elements are falsy, returns undefined 23export function classNames(...args: ArgType[]) { 24 // NOTE: This function is optimized for efficiency. Be very careful when 25 // making changes & make sure to benchmark. 26 let result = ''; 27 for (let i = 0; i < args.length; ++i) { 28 // eslint-disable-next-line @typescript-eslint/strict-boolean-expressions 29 if (args[i]) { 30 result += result ? ' ' + args[i] : args[i]; 31 } 32 } 33 return result || undefined; 34} 35