fp-object-transform

Object Transform

Introduction:

A small library to do object transforms. Mostly for use with functional programming pipelines and streams. The arguments are 'reversed' to be able to do meaningful partial application / currying.

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.transformSync(fn, object)

Transform the properties of an object based on a transform function fn

Arguments

• fn(result, value, key) - This gets called for all properties of the object, and the result should be mutated to the desired result. No explicit return necessary.
• object - The original object that is to be transformed.

Example

var obtr = require('fp-object-transform');
 
var words = {
  a: 'hello',
  b: 'world'
};
 
var transformed = obtr.transformSync(function(result, value, key) {
  result[key] = value.split('').reverse().join('');
}, words);
// {
//   a: 'olleh',
//   b: 'dlrow'
// }

---

.transformToSync(transforms, object)

Transform the properties of an object based on an object describing transforms on specific properties. The value of the property is used as input for the transform

Arguments

• transforms - An object specifying the transforms to be applied.
• object - The original object that is to be transformed.

Example

var obtr = require('fp-object-transform');
 
var reverse = function(str) {
  return str.split('').reverse().join('');
};
 
var words = {
  a: 'hello',
  b: 'world',
  foo: 'bar',
  bar: {
    baz: 'qux'
  }
};
 
var transforms = {
  a: reverse,
  b: reverse,
  bar: {
    baz: reverse
  }
};
 
var transformed = obtr.transformToSync(transforms, words);
// {
//   a: 'olleh',
//   b: 'dlrow',
//   foo: 'bar',
//   bar: {
//     baz: 'xuq'
//   }
// }

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.copyToFrom(specs, object)

Copy object properties to new properties on the same object, with support for string literals

Arguments

• specs - A string or an array of strings describing what to copy and where to put it.
• object - The original object that is to be transformed.

Example

var obtr = require('fp-object-transform');
 
var original = {
  name: 'Eirik',
  birth: {
    year: 1986
  },
  list: [{
    count: 1
  }]
};
 
var specs = {
  newField: 'name',
  newField2: {
    nestedField: 'name',
    nestedField2: {
      birthYear: 'birth.year'
    }
  },
  birthYear: 'birth.year',
  firstListElement: 'list[0].count'
};
 
var transformed = obtr.copyToFrom(specs, original);
// { 
//   name: 'Eirik',
//   birth: { year: 1986 },
//   list: [ { count: 1 } ],
//   newField: 'Eirik',
//   newField2: { nestedField: 'Eirik', nestedField2: { birthYear: 1986 } },
//   birthYear: 1986,
//   firstListElement: 1
// }

---

.transform(fn, object, callback)

(Asyncronous version) Transform the properties of an object based on a transform function fn.

Arguments

• fn(result, value, key, callback) - This gets called for all properties of the object, and the result should be mutated to the desired result. Invoke callback with an error or null when done.
• object - The original object that is to be transformed.
• callback(err, result) - a final callback to be called with the result or an error.

Example

var obtr = require('fp-object-transform');
 
var words = {
  a: 'hello',
  b: 'world'
};
 
obtr.transform(function(result, value, key, callback) {
  result[key] = value.split('').reverse().join('');
  callback();
}, words, function(err, transformed) {
  console.log(transformed);
  // {
  //   a: 'olleh',
  //   b: 'dlrow'
  // }
});

---

.transformTo(transforms, object)

(Asyncronous version) Transform the properties of an object based on an object describing transforms on specific properties. The value of the property is used as input for the transform.

Arguments

• transforms - An object specifying the transforms to be applied.
• object - The original object that is to be transformed.
• callback(err, result) - a final callback to be called with the result or an error.

Example

var obtr = require('fp-object-transform');
 
var reverse = function(input, callback) {
  callback(null, input.split('').reverse().join(''));
}
 
var words = {
  a: 'hello',
  b: 'world',
  foo: 'bar',
  bar: {
    baz: 'qux'
  }
};
 
var transforms = {
  a: reverse,
  b: reverse,
  bar: {
    baz: reverse
  }
};
 
obtr.transformTo(transforms, words, function(err, transformed) {
  console.log(transformed);
  // {
  //   a: 'olleh',
  //   b: 'dlrow',
  //   foo: 'bar',
  //   bar: {
  //     baz: 'xuq'
  //   }
  // }
});

---

.deriveToSync(derivatives, object)

Transform the properties of an object based on an object describing transforms on specific properties. The value of the property is used as input for the transform

This is really just a shorthand for doing .copyToFrom and .transformToSync in sequence.

Arguments

• derivatives - An object specifying the derivatives to be applied.
• object - The original object that is to be transformed.

Example

var obtr = require('fp-object-transform');
 
var reverse = function(str) {
  return str.split('').reverse().join('');
};
 
var words = {
  a: 'hello',
  b: 'world',
  foo: 'bar',
  bar: {
    baz: 'qux'
  }
};
 
var derivatives = {
  b: ['b', reverse];
  newField: ['bar.baz', reverse],
};
 
var transformed = obtr.deriveToSync(derivatives, words);
// {
//   a: 'hello',
//   b: 'dlrow',
//   foo: 'bar',
//   bar: {
//     baz: 'qux'
//   },
//   newField: 'xuq'
// }

---

.deriveTo(derivatives, object)

(Asynchronous version) Transform the properties of an object based on an object describing transforms on specific properties. The value of the property is used as input for the transform

This is really just a shorthand for doing .copyToFrom and .transformTo in sequence.

Arguments

• derivatives - An object specifying the derivatives to be applied.
• object - The original object that is to be transformed.

Example

var obtr = require('fp-object-transform');
 
var reverse = function(input, callback) {
  callback(null, input.split('').reverse().join(''));
}
 
var words = {
  a: 'hello',
  b: 'world',
  foo: 'bar',
  bar: {
    baz: 'qux'
  }
};
 
var transforms = {
  b: ['b', reverse];
  newField: ['bar.baz', reverse],
};
 
obtr.deriveTo(transforms, words, function(err, transformed) {
  console.log(transformed);
  // {
  //   a: 'hello',
  //   b: 'dlrow',
  //   foo: 'bar',
  //   bar: {
  //     baz: 'qux'
  //   },
  //   newField: 'xuq'
  // }
});

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