0.8.0 • Public • Published



Utility library for object structure conversion.


npm install --save parse-js


A parser always starts with a call to parse(), next you can chain any transformer of of that as is required.

const parse = require('parse-js');

parse().bool().parse('true'); // true
    atest: 'test123',
    btest: 'test456'
}); // { atest: 'test123' }

Parse also accepts one argument which can be the key to extract from the object to parse. Passing this argument will automatically chain the select transformer.

const parse = require('parse-js');

    'a-key': 'a-value',
    'some-key': 'some-value'
}); // 'a-value'

This is equivalent to:

const parse = require('parse-js');

    'a-key': 'a-value',
    'some-key': 'some-value'
}); // 'a-value'



Whenever .parse() is called the configured chain will be executed on the first argument data.

If the option direction is set to REVERSE this method will simply return the data argument as is without modifying it.


parse('test-key').base64().parse({ 'test-key': 'SGVsbG8gV29ybGQ=' });
// Hello World



The .reverse() method will apply all the reverse methods of each transformer and attempts to reassembly the original object based on the sourceData.


parse('test-key').base64().reverse('Hello World');
// {
//    'test-key': 'SGVsbG8gV29ybGQ='
// }


.transform(parser, [reverser])

This method allows you to chain your own custom parser and reverser. Both the parser and reverser take one argument as input which is the value to be parsed or reversed.

Instead of supplying both methods as separator arguments you can also pass the parser and reverser as an object with both the keys defined.


// Increment / decrement transformer
function parser(v) { return v + 1; };
function reverser(v) { return v - 1; };

parse().transform(parser, reverser).parse(1); // 2
parse().transform(parser, reverser).reverse(3); // 2

// or alternatively
const transformer = {
    parser: parser,
    reverser: reverser

parse().transform(transformer).parse(1); // 2



The .chain() method allows your to create pre-defined chains which can be easily re-used for different parsers.


This example created a pre-defined one-way base64 parser.

function base64_decode(p) {
    return p.base64().setOption('direction', 'PARSE');

    .parse({ 'some-key': 'SGVsbG8gV29ybGQ=' }); // Hello World


Both parse-js instances and the parse method have methods to set global options setOption and getOption, these can be used to configure transformers that have global settings.

Parse.setOption(key, value);

parse().setOption(key, value);

Currently only the multilingual transformer has such options.

The behaviour of a parse-js chain can be altered using the direction option which configures in which directions the transformers should be applied. When set to PARSE the .reverse() calls will not touch the data supplied. Similarly setting direction to REVERSE will leave the data untouched as .parse() is called. By default both directions are enabled and the option is set to ANY.




Selects a value from the object provided to the final .parse() call, the key supplied here can be any key supported by lodash get.


parse().default(defaultValue, reverseDefaultValue)

Sets a default value when either the selected value or the reversed value is undefined.

  • defaultValue the value to return whenever the selected value is undefined
  • reverseDefaultValue the value to return whenever the value to reverse is undefined



Only selects those properties from an object that match valueToMatch.

  • valueToMatch can either be a string or a regular expression.


parse().rename(nameParser, nameReverser);

Converts key names using a function for each transition.

  • nameParser(key, value) will be called with the original key and value as arguments and should return the new key.
  • nameReverser(key, value) will be called with the generated key and the value set on the object and should return the key to which this value should be written.



Map will walk each key of a select value and call the callback function with a new instance of parse-js specific to that key.

  • callback(parse) will be called with a new instance of parse for each key, which you can then customize by adding new chained transformers.


parse().map(p => p.number()).parse({
    a: '123',
    b: 0,
    c: '12.222,3'
}); // { a: 123, b: 0, c: 12222.3 }


parse().group(regex, key, index)

group will walk over each key of an object matching it against regular expression regex. If it matches the value will be stored at result[match[key]][match[index]], where match is the set of matching groups from regex. If a key does not match the regex it will be re-attached to the object untouched.

  • The key argument should be set to the index of the matching group that selects the new key to use.
  • The index arguments should be set to the index of the matching group that selects the sub-key under which to store the value.


parse().group(/(a|b|c)-(name|value)/, 1, 2).parse({
    'a-name': 'a-name',
    'b-name': 'b-name',
    'c-value': 'c-value',
    'b-value': 'b-value',
    'c-name': 'c-name',
    'a-value': 'a-value'
// {
//    a: { value: 'a-value', name: 'a-name' },
//    b: { value: 'b-value', name: 'b-name' },
//    c: { value: 'c-value', name: 'c-name' }
// }


parse().oneOf(parsers, [options = {}])

oneOf lets you define multiple parsers of which the first in the list with a result that is valid according to the test option will be used.

  • parsers an array of parse-js parsers to go through.
  • options
    • test a method which returns true if the result of a parser is valid. (default: !isEmpty(v))
    • reverseAll controls whether all parsers are called to reverse the value or only the first one. (default: true)


]).parse({ 'firstName': 'John', email: '' });
// 'John'


parse().equals(valueToMatch, [options = {}])

If the selected value matched valueToMatch it will return true, if it does not it will return false.

  • valueToMatch can be either a regular expressions, function or simply any value.
  • options can be used to change behaviour of the transformer
    • strict will ensure === comparison is used when comparing. (default: false).
    • reverse can be set to the value that should be set when reversing a true value. (default: valueToMatch)


parse().equals('some-value').parse('some-other-value'); // false
parse().equals('some-value').parse('some-value'); // true


parse().constant(constantValue, [options = {}])

Always returns constantValue from parse and reverse. The value returned from reverse can be different from constantValue using the reverseValue option.

  • constantValue the value that will be returned by this transformer.
  • options
    • reverseValue If reverse should return a different value it can be configured using this option.


parse().constant('a-constant').parse('some-value'); // 'a-constant'
parse().constant('a-constant', {
    reverseValue: 'b-constant'
}).reverse('some-value'); // 'b-constant'


parse().date([nowOnInvalid = false])

Converts the selected value into a javascript date object.

  • nowOnInvalid If set to true will return the current date-time whenever the value being parsed is not a valid date.


parse().bool([options = {}])

Converts the selected value to a boolean value.

  • options
    • defaultValue when the value being parsed is undefined what should be set as the default value.
    • reverseTo configures the datatype to which the boolean values are reversed. Valid options are BOOLEAN, STRING or NUMBER.


parse().number([options = {}])

Converts the selected value to a number.

  • options
    • NaNValue the value that will be set when the selected value can not be converted. (default: 0)
    • normalizer a function used to normalize strings to number-like strings. The default handles removing multiple comma or dots in the string.
    • base the base in which the value is expressed. (default: 10)
    • decimalSeparator the sign to use as decimal separator (. or ,), if not configured, the library does its best to auto-detect


parse().string([options = {}])

Converts the selected value to a string. The selected value will be concatenated with an empty string which will call the toString() method of most values.

  • options
    • defaultValue the value to return whenever the selected value is undefined.


parse().switch(cases, parseSelector, reverseSelector)

Selects a different parser from the cases object by looking up the value at parseSelector / reverseSelector in the cases object and executing it.

If the cases object does not define a key for the value at returned by the selector, the _default_ key will be called if defined. If neither of these exist undefined will be returned.

Both parseSelector and reverseSelector can be any key supported by lodash get or a method which is passed the object to transform and the root object of this transform. Passing null or undefined will disable the selector and .switch() will always return undefined.

  • cases an object containing the different possible values for the field at selector.
  • parseSelector a key that specifies which key to look up in the cases object when performing a .parse() operation.
  • reverseSelector a key that specifies which key to look up in the cases object when performing a .reverse() operation.


        'string': parse('value').string(),
        'number': parse('value').number(),
        '_default_': parse('value').string()
    }, 'type', (v) => typeof v)
        'test-key': {
            type: 'number',
            value: '123'
    // 123


parse().array([options = {}])

This transformer will ensure that the selected value will be converted to an array. Whenever this fails it will return an empty array.

  • options
    • mode the methods that are allowed to be used to convert values to arrays. (default: ANY). Valid options are ANY, JSON and SEPARATOR.
    • separator the separator to be used when mode is set to ANY or SEPARATOR. (default: ,)


parse().base64([options = {}])

Handles conversion from and to base64 strings.

  • options
    • allowBinary when this option is set to true the isPrintable check will be disabled. Because of this any valid base64 formatted string will be decoded.


parse().json([options = {}])

Converts the selected value from and to a JSON string.

  • options
    • defaultValue will be returned whenever no valid JSON string is selected.



A specification is an object that has the desired properties of the target format, where the values are the parsers that generate the value to store with this property. This allows a source format to be converted to the desired format using parse-js.

  • specification an object containing key - parser combinations.


    one: parse('two'),
    two: parse('one').number(),
    three: parse('four').array(),
    nested: {
        one: parse('one'),
        two: parse('four').json()
}).parse({ one: '15.333.23', two: 'two', four: '[1,2,3,4,5]' });
// {
//     one: 'two',
//     two: 15333.23,
//     three: [1, 2, 3, 4, 5],
//     nested: {
//         one: '15.333.23',
//         two: [1, 2, 3, 4, 5]
//     }
// }



Will group keys with language suffixes as defined by group()

  • languages configures the languages that are supported. This option can also be set using the setOption() method of the parse-js instance or Parse.setOption(). When using setOption() this option is configured using the key multilingual.languages.


parse().multilingual(['en', 'nl', 'fr', 'de']).parse({
    keyEn: 'english text',
    keyNl: 'dutch text'
// {
//     key: { en: 'english text', nl: 'dutch text' }
// }



Selects keys that start with prefix and removes that prefix from the target object.

  • prefix the prefix that keys should contain and that will be removed.


    atest: 'value-1',
    test1: 'value-2',
    test2: 'value-3'
// { 1: 'value-2', 2: 'value-3' }


We really appreciate any contribution you would like to make, so don't hesitate to report issues or submit pull requests.


This project is released under a MIT license.

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