| // Copyright (C) 2023 The Android Open Source Project |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| |
| // It's common to want to have a class depending on a boolean flag, in which |
| // case we use `flag && className` which evaluates to either false or a string, |
| // which is why false is included in definition of ArgType. |
| type ArgType = string | false | undefined | ArgType[]; |
| |
| // Join class names together into valid HTML class attributes |
| // Falsy elements are ignored |
| // Nested arrays are flattened |
| // If all elements are falsy, returns undefined |
| export function classNames(...args: ArgType[]): string | undefined { |
| const filtered = args.flat().filter((x) => x); |
| if (filtered.length === 0) { |
| return undefined; |
| } else { |
| return filtered.join(' '); |
| } |
| } |
