fixed-width-parser is a node module for parsing data to and from fixed width string formats.
npm install fixed-width-parserconst { FixedWidthParser } = require('fixed-width-parser');
const fixedWidthParser = new FixedWidthParser([
{
type: 'int',
name: 'age',
start: 0,
width: 2,
},
{
name: 'name',
start: 2,
width: 12,
},
]);
const input = `42 bob
21 alice
33 jeff`;
const result = fixedWidthParser.parse(input);result is an array with the following content:
[
{
"age": 42,
"name": "bob"
},
{
"age": 21,
"name": "alice"
},
{
"age": 33,
"name": "jeff"
}
]interface IParseOptions {
/**
* Value to return when value parses as falsy:
*
* - `'undefined'` = `undefined`
* - `'null'` = `null`
* - `'passthrough'` = return the original falsy value
*
* If the value is not defined the default behavior is to passthrough
*/
falsyFallback: FalsyFallback;
}const { FixedWidthParser } = require('fixed-width-parser');
const fixedWidthParser = new FixedWidthParser([
{
type: 'int',
name: 'age',
start: 0,
width: 2,
},
{
name: 'name',
start: 2,
width: 12,
},
]);
const input = [
{
age: 42,
name: 'bob',
},
{
age: 21,
name: 'alice',
},
{
age: 33,
name: 'jeff',
},
];
const result = fixedWidthParser.unparse(input);result is a string with the following content:
42 bob
21 alice
33 jeff
When initializing a new instance of the FixedWidthParser class, you must provide an array of parse
configs. These configs define how to convert between lines of text and json objects by providing a
mapping between segments of text and object keys.
All parse configs share the following properties:
interface IBaseParseConfig {
// default: 'string'
type?: string;
// number of characters used in fixed width string for this field
// required
width: number;
// zero-based index of starting character in fixed width string for this field
// required
start: number;
// default: 'start'
padPosition?: 'start' | 'end';
// default: ' '
padString?: string;
// value to use when unparsing if field in input is undefined
default?: string | number;
// overrides FixedWidthParser.defaults.truncate
truncate?: boolean;
// value to return if the parsed value is falsy
// this will override the more general behavior in parse options
// default: IParseOptions.falsyFallback value
falsyFallback?: 'undefined' | 'null' | 'passthrough';
}An explicit type property can be provided in each parse config to specify what data types to use
for values parsed from strings. Several of these data types require additional properties to be
provided to fully define how parse/unparse values.
// Default config type
interface IStringParseConfig {
type: 'string';
// key name in JSON input/output
// required
name: string;
}// Will parse using parseInt
interface IIntegerParseConfig {
type: 'int';
// key name in JSON input/output
// required
name: string;
// integer between 2 and 36 that represents the radix of the string
// default: 10
radix?: number;
// When parsing and unparsing, there may be an error that the value given is not
// an integer. This is a way of the parser to work around this issue. Give an option here
// to have the parser do the following when encountering a non-int as an int-type
// ceil: performs Math.ceil() on the data
// floor: performs Math.floor() on the data
// round: performs Math.round() on the data
// error: Will throw an error if the data is not an int
// default: floor
mend?: 'ceil' | 'floor' | 'round' | 'error';
}// Will parse using Number() after injecting a decimal if necessary
interface IFloatParseConfig {
type: 'float';
// key name in JSON input/output
// required
name: string;
// whether or not to insert a decimal in formatted string
// default: true
insertDecimal?: boolean;
// number of decimal places to assume if no decimal is present
// default: 2
decimalCount?: number;
}interface IDateParseConfig {
type: 'date';
// key name in JSON input/output
// required
name: string;
// required
// unicode date field symbol pattern
fixedWidthFormat: string;
// required
// unicode date field symbol pattern
jsonFormat: string;
// attempt to parse raw value before failing if trimmed value is not parsable as a Date
// default: false
tryParsingRawValueBeforeFallback: boolean;
}interface IBooleanParseConfig {
type: 'bool';
// key name in JSON input/output
// required
name: string;
// required
// fixed width string value to parse as true
trueValue: string;
// required
// fixed width string value to parse as false
falseValue: string;
}interface ISkipParseConfig {
type: 'skip';
}When constructing a new FixedWidthParser instance the provided parse config will be validated. If
any errors are detected an array of validation errors will be thrown to help you find and correct
the invalid configs.
interface IParseConfigValidationError {
// Index of the invalid parse config
index: number;
// The invalid parse config
config: ParseConfig;
// List of issues detected in the parse config
errors: string[];
}interface IFixedWidthParserOptions {
// Allows truncating values that are too long instead of throwing.
//
// This value can be overridden by the 'truncate' option in individual parse configs.
// default: true
truncate?: boolean;
// If provided, enables an additional validation of the provided parse config
// map. If sum of all `width` values in the parse config map do not match this
// value, then the an error is thrown.
expectedFullWidth?: number;
// Specifies if only certain characters should be allowed, and if so, which
// ones; all other characters are removed.
// default: undefined - which allows all characters
characterWhitelist?: ICharacterWhitelist;
} // Allow upper and lower case characters from the Latin alphabet:
// AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz
alpha?: boolean;
// Allow the ten digits:
// 1234567890
numeric?: boolean;
// Allow commonly used punctuation and symbols including spaces (' ')
// ~ `!@#$%^&*()-_=+{}[]\|/?:;'"<>,.
special?: boolean;
// Allow other characters beyond the Basic Latin Unicode block such as
// - control characters: \u0000 \f �
// - emojis 😀 🎉 🚀
// - other symbols and special characters: ⍺è¶
extended?: boolean;
// Allow each character in the given array. Each item should include only 1 character.
// The characters listed here take priority over other options, for example, if
// numeric characters are not allowed, but 0 is in the list of 'other'
// characters, all numeric characters will be omitted except 0.
other?: string[];By default any logs from the parser will be handled by the built in console logger. You can
optionally provide your own ILogger compatible logger to process logs.
const { FixedWidthParser, ILogger } = require('fixed-width-parser');
const myLogger: ILogger = {
warn: (...data: any[]) => console.warn(data);
}
const fixedWidthParser = new FixedWidthParser(
[
{
type: 'int',
name: 'age',
start: 0,
width: 2,
},
{
name: 'name',
start: 2,
width: 12,
},
],
undefined, // options
myLogger, // Default: console
);A huge thanks to @SteveyPugs for his work on fixy which served as inspiration for
fixed-width-parser! fixed-width-parser started out as a fork of fixy and evolved into its own
library when I got carried away and implemented a new high-level API.
Another huge thanks to @wk-davis for her help with concept discussions and ongoing development help!