@bscotch/mpath

Forked from the popular mpath module, rewritten in Typescript for modern Node targets (uses ECMAScript Modules).

{G,S}et JavaScript object values using MongoDB-like path notation.

Getting

import mpath from "mpath";

const obj = {
    comments: [
      { title: 'funny' },
      { title: 'exciting!' }
    ]
}

mpath.get('comments.1.title', obj) // 'exciting!'

mpath.get supports array property notation as well.

const obj = {
    comments: [
      { title: 'funny' },
      { title: 'exciting!' }
    ]
}

mpath.get('comments.title', obj) // ['funny', 'exciting!']

Array property and indexing syntax, when used together, are very powerful.

const obj = {
  array: [
      { o: { array: [{x: {b: [4,6,8]}}, { y: 10} ] }}
    , { o: { array: [{x: {b: [1,2,3]}}, { x: {z: 10 }}, { x: 'Turkey Day' }] }}
    , { o: { array: [{x: {b: null }}, { x: { b: [null, 1]}}] }}
    , { o: { array: [{x: null }] }}
    , { o: { array: [{y: 3 }] }}
    , { o: { array: [3, 0, null] }}
    , { o: { name: 'ha' }}
  ];
}

const found = mpath.get('array.o.array.x.b.1', obj);

console.log(found); // prints..

    [ [6, undefined]
    , [2, undefined, undefined]
    , [null, 1]
    , [null]
    , [undefined]
    , [undefined, undefined, undefined]
    , undefined
    ]

Field selection rules:

The following rules are iteratively applied to each segment in the passed path. For example:

const path = 'one.two.14'; // path
'one' // segment 0
'two' // segment 1
14    // segment 2

• 1. when value of the segment parent is not an array, return the value of parent.segment
• 2. when value of the segment parent is an array
  • a) if the segment is an integer, replace the parent array with the value at parent[segment]
  • b) if not an integer, keep the array but replace each array item with the value returned from calling get(remainingSegments, item) or undefined if falsey.

Maps

mpath.get also accepts an optional map argument which receives each individual found value. The value returned from the map function will be used in the original found values place.

const obj = {
    comments: [
      { title: 'funny' },
      { title: 'exciting!' }
    ]
}

mpath.get('comments.title', obj, function (val) {
  return 'funny' == val
    ? 'amusing'
    : val;
});
// ['amusing', 'exciting!']

Setting

const obj = {
    comments: [
      { title: 'funny' },
      { title: 'exciting!' }
    ]
}

mpath.set('comments.1.title', 'hilarious', obj)
console.log(obj.comments[1].title) // 'hilarious'

mpath.set supports the same array property notation as mpath.get.

const obj = {
    comments: [
      { title: 'funny' },
      { title: 'exciting!' }
    ]
}

mpath.set('comments.title', ['hilarious', 'fruity'], obj);

console.log(obj); // prints..

  { comments: [
      { title: 'hilarious' },
      { title: 'fruity' }
  ]}

Array property and indexing syntax can be used together also when setting.

const obj = {
  array: [
      { o: { array: [{x: {b: [4,6,8]}}, { y: 10} ] }}
    , { o: { array: [{x: {b: [1,2,3]}}, { x: {z: 10 }}, { x: 'Turkey Day' }] }}
    , { o: { array: [{x: {b: null }}, { x: { b: [null, 1]}}] }}
    , { o: { array: [{x: null }] }}
    , { o: { array: [{y: 3 }] }}
    , { o: { array: [3, 0, null] }}
    , { o: { name: 'ha' }}
  ]
}

mpath.set('array.1.o', 'this was changed', obj);

console.log(require('util').inspect(obj, false, 1000)); // prints..

{
  array: [
      { o: { array: [{x: {b: [4,6,8]}}, { y: 10} ] }}
    , { o: 'this was changed' }
    , { o: { array: [{x: {b: null }}, { x: { b: [null, 1]}}] }}
    , { o: { array: [{x: null }] }}
    , { o: { array: [{y: 3 }] }}
    , { o: { array: [3, 0, null] }}
    , { o: { name: 'ha' }}
  ];
}

mpath.set('array.o.array.x', 'this was changed too', obj);

console.log(require('util').inspect(obj, false, 1000)); // prints..

{
  array: [
      { o: { array: [{x: 'this was changed too'}, { y: 10, x: 'this was changed too'} ] }}
    , { o: 'this was changed' }
    , { o: { array: [{x: 'this was changed too'}, { x: 'this was changed too'}] }}
    , { o: { array: [{x: 'this was changed too'}] }}
    , { o: { array: [{x: 'this was changed too', y: 3 }] }}
    , { o: { array: [3, 0, null] }}
    , { o: { name: 'ha' }}
  ];
}

Setting arrays

By default, setting a property within an array to another array results in each element of the new array being set to the item in the destination array at the matching index. An example is helpful.

const obj = {
    comments: [
      { title: 'funny' },
      { title: 'exciting!' }
    ]
}

mpath.set('comments.title', ['hilarious', 'fruity'], obj);

console.log(obj); // prints..

  { comments: [
      { title: 'hilarious' },
      { title: 'fruity' }
  ]}

If we do not desire this destructuring-like assignment behavior we may instead specify the $ operator in the path being set to force the array to be copied directly.

const obj = {
    comments: [
      { title: 'funny' },
      { title: 'exciting!' }
    ]
}

mpath.set('comments.$.title', ['hilarious', 'fruity'], obj);

console.log(obj); // prints..

  { comments: [
      { title: ['hilarious', 'fruity'] },
      { title: ['hilarious', 'fruity'] }
  ]}

Field assignment rules

The rules utilized mirror those used on mpath.get, meaning we can take values returned from mpath.get, update them, and reassign them using mpath.set. Note that setting nested arrays of arrays can get unweildy quickly. Check out the tests for more extreme examples.

Maps

mpath.set also accepts an optional map argument which receives each individual value being set. The value returned from the map function will be used in the original values place.

const obj = {
    comments: [
      { title: 'funny' },
      { title: 'exciting!' }
    ]
}

mpath.set('comments.title', ['hilarious', 'fruity'], obj, function (val) {
  return val.length;
});

console.log(obj); // prints..

  { comments: [
      { title: 9 },
      { title: 6 }
  ]}

Custom object types

Sometimes you may want to enact the same functionality on custom object types that store all their real data internally, say for an ODM type object. No fear, mpath has you covered. Simply pass the name of the property being used to store the internal data and it will be traversed instead:

import mpath from "mpath";

const obj = {
    comments: [
      { title: 'exciting!', _doc: { title: 'great!' }}
    ]
}

mpath.get('comments.0.title', obj, '_doc')            // 'great!'
mpath.set('comments.0.title', 'nov 3rd', obj, '_doc')
mpath.get('comments.0.title', obj, '_doc')            // 'nov 3rd'
mpath.get('comments.0.title', obj)                    // 'exciting'

When used with a map, the map argument comes last.

mpath.get(path, obj, '_doc', map);
mpath.set(path, val, obj, '_doc', map);