copy-props

Copy properties deeply between two objects.

Install

$ npm i copy-props

Usage

• Load this module :

  const copyProps = require('copy-props');

• Copy src to dst simply (and return dst) :

  var src = { a: 1, b: { b1: 'bbb' }, c: 'ccc' };
  var dst = { a: 2, b: { b1: 'xxx', b2: 'yyy' } };
  
  copyProps(src, dst);
  // => { a: 1, b: { b1: 'bbb', b2: 'yyy' }, c: 'ccc' }

• Copy src to dst with property mapping (and return dst) :

  var src = { a: 1, b: { b1: 'bbb' }, c: 'ccc', d: 'ddd' };
  var dst = { f: { a: 2, b1: 'xxx', b2: 'yyy' }, e: 'zzz' };
  
  copyProps(src, dst, {
    a: 'f.a',
    'b.b1': 'f.b.b1',
    'b.b2': 'f.b.b2',
    'c': 'f.c',
  });
  // => { f: { a: 1, b1: 'bbb', b2: 'yyy', c: 'ccc' }, e: 'zzz' }

• Copy src to dst with convert function (and return dst) :

  var src = { a: 1, b: { b1: 'bbb' } };
  var dst = { a: 0 };
  
  copyProps(src, dst, function(value, keyChain) {
    if (keyChain === 'a') {
      return value * 2;
    }
    if (keyChain === 'b.b1') {
      return value.toUpperCase();
    }
  });
  // => { a: 2, b: { b1: 'BBB' } }

• Can use an array instead of a map as property mapping :

  var src = { a: 1, b: { c: 'CCC' }, d: { e: 'EEE' } };
  var dst = { a: 9, b: { c: 'xxx' }, d: { e: 'yyy' } };
  var fromToProps = [ 'a.b.c', 'd.e' ];
  copyProps(src, dst, fromToProps);
  // => { a: 1, b: { c: 'CCC' }, d: { e: 'EEE' } }

• Can copy reversively (from dst to src) by option { reverse: true } (and return src):

  var src = { a: 1, b: { b1: 'bbb' }, c: 'ccc' };
  var dst = { a: 2, b: { b1: 'xxx', b2: 'yyy' } };
  
  copyProps(src, dst, true);
  // => { a: 2, b: { b1: 'xxx', b2: 'yyy' }, c: 'ccc' }

  var src = { a: 1, b: { b1: 'bbb' }, c: 'ccc', d: 'ddd' };
  var dst = { f: { a: 2, b1: 'xxx', b2: 'yyy' }, e: 'zzz' };
  
  copyProps(src, dst, {
    a: 'f.a',
    'b.b1': 'f.b1',
    'b.b2': 'f.b2',
    'c': 'f.c',
  }, { reverse: true });
  // => { a: 2, b: { b1: 'bbb', b2: 'yyy' }, c: 'ccc', d: 'ddd' }

• Can reject to copy null value by option { rejectNull: true } :

  var src = { a: 8, b: { c: -1, d: null } };
  var dst = { a: 1, b: { c:  2, e: 4 } };
  
  copyProps(src, dst, function(v) {
    return (typeof v !== 'number' || v < 0) ? null : v;
  }, { rejectNull: true });
  // => { a: 8, b: { c: 2, e: 4 } }

  This opts must be passed at the place of the 4rd argument or later.

  So, when you use the opts and don't use neither fromToProps nor converter, write the code as follows:

  var src = { a: 8, b: { c: -1, d: null } };
  var dst = { a: 1, b: { c:  2, e: 4 } };
  
  copyProps(src, dst, null, { rejectNull: true });
  // => { a: 8, b: { c: -1, e: 4 } }

API

copyProps(src, dst [, fromToProps] [, converter] [, opts]) => object

Copy properties of src to dst deeply. If fromToProps is given, it is able to copy between different properties. If converter is given, it is able to convert the terminal values.

• Arguments:

  • src [object] : a source object of copy.
  • dst [object] : a destinate object of copy.
  • fromToProps [object | array] : an object mapping properties between src and dst. (optional)
  • converter [function] : a function to convert terminal values in src. (optional)
  • opts [object] : an option object which specifys copy's behaviors (optional)

• Return [object] : dst object after copying.

Format of fromToProps

fromToProps is a non-nested key-value object. And the keys are property key chains of src and the values are property key chains of dst. The key chain is a string which is concatenated property keys on each level with dots, like 'aaa.bbb.ccc'.

The following example copys the value of src.aaa.bbb.ccc to dst.xxx.yyy.

copyProps(src, dst, {
  'aaa.bbb.ccc' : 'xxx.yyy'
})

fromToProps can be an array. In that case, the array works as a map which has pairs of same key and value.

API of converter

converter(value, keyChain) => any

converter is a function to convert terminal values of propeerties of src.

• Arguments:

  • value [any] : a property value to be converted.
  • keyChain [string] : a string of property keys concatenated with dots.

• Return: [any] : converted value.

Properties of opts

opts can have following properties:

• reverse [boolean] : Copys reversively from dst to src and returns src object. fromToProps is also reversively used from value to key. This default value is false.
• rejectNull [boolean] : if this option is true, a value of a source object or a return value of converter is not copied when the value is null. The default value is true.

License

MIT