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Basic TypeScript friendly validate/cast function based validation library experiment
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| import Axios, { AxiosError } from "axios"; | |
| // Casting/validation library | |
| class DataInputError extends Error { | |
| path: string[] = []; | |
| static isDataInputError(error: unknown): error is DataInputError { | |
| return error ? error instanceof DataInputError : false; | |
| } | |
| wrapParent(propertyName: string): DataInputError { | |
| const parent = new DataInputError(this.message); | |
| parent.path = [propertyName, ...this.path]; | |
| // @note Needs to also modify the message in some way to include and update the path | |
| return parent; | |
| } | |
| } | |
| function validateObject<TOut extends {}>(shape: { | |
| [key in keyof TOut]: (data: unknown) => TOut[key]; | |
| }): (data: unknown) => TOut { | |
| return (data: unknown): TOut => { | |
| if (data === null || typeof data !== "object") | |
| throw new DataInputError("is not an object"); | |
| const out: any = {}; | |
| for (const key in shape) { | |
| const propertyValidator = shape[key]; | |
| try { | |
| const outValue = propertyValidator(key in data ? data : undefined); | |
| if (outValue !== undefined) out[key] = outValue; | |
| } catch (e) { | |
| if (DataInputError.isDataInputError(e)) { | |
| throw e.wrapParent(key); | |
| } else { | |
| throw e; | |
| } | |
| } | |
| } | |
| return out; | |
| }; | |
| } | |
| function castObject<TOut extends {}>(shape: { | |
| [key in keyof TOut]: (data: unknown) => TOut[key]; | |
| }): (data: unknown) => TOut { | |
| const validate = validateObject(shape); | |
| return (data: unknown): TOut => { | |
| return validate(data === null || typeof data !== "object" ? {} : data); | |
| }; | |
| } | |
| // Validation functions that can be user defined or provided by the library as helpers | |
| function string(): (data: unknown) => string { | |
| return () => { | |
| if (typeof data !== "string") throw new DataInputError("is not a string"); | |
| return data; | |
| }; | |
| } | |
| // Wrappers could be used to add behaviours like optional properties | |
| function optional<T>( | |
| cast: (data: unknown) => T | |
| ): (data: unknown) => T | undefined { | |
| return (data: unknown): T | undefined => { | |
| return data == null ? undefined : cast(data); | |
| }; | |
| } | |
| // Input data in an unknown format (query string data, form data, etc) | |
| const data: unknown = { foo: { bar: "baz" } }; | |
| // The only actual user code used for casting the data | |
| const cast = castObject({ | |
| foo: castObject({ | |
| bar: optional(string()), | |
| }), | |
| error: (err) => (Axios.isAxiosError(err) ? err : undefined), | |
| }); | |
| const output = cast(data); | |
| interface TheData { | |
| foo: { bar?: string }; | |
| error?: AxiosError; | |
| } | |
| const theData: TheData = output; |
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