Nested Read Write

A powerful tool to select and update properties nested deep within an object.

Example

const nrw = require('nested-read-write')
const path = nrw.parse('users[].name')
path.read({
  users: [
    {name: "Alex", age: 25},
    {name: "Sam", age: 30}
  ]
})
// returns ["Alex", "Sam"]

path.write({}, ["Alice", "Bob"])
// returns {users: [{name: "Alice"}, {name: "Bob"}]}

Interface

nrw.parse(path)

Creates a Path object from path string.

Path.prototype.read(src)

Returns value from src according to Path object.

Path.prototype.write(dest, value)

Mutates dest with value according to Path object, and returns mutated dest.

Path.prototype.standardize()

Cleans up the Path object by removing redundant operations. (E.g. "&.a" would standardize to "a")

Path.prototype.toString()

Rebuilds the path string. It should be nearly identical, but with whitespace removed.

Quick Guide

| Operation | Read Description | Write Description | | - | - | - | | & | Gets relative source | invalid | | .name | Gets name property | Sets name property | | [name] | Gets name property | Sets name property | | [path] | Gets value at path | Sets value at path | | [ ] | Gets shallow array copy | Sets elements of relative source to elements of value | | | arrayop | Gets flattened array | invalid | | [begin:end:step] | Gets slice | invalid | | [n1, n2, n3] | Gets array at indices ni | Sets indices ni to value[i] | | [path1, path2, path3] | Gets array of pathi values | Writes value[i] to pathi | | [@] | invalid | Concatenates values to array | | [@n] | invalid | Inserts values into array before index n | | { } | Gets shallow object copy | Assigns entries of value to relative source | | { path1, path2, path3 } | Gets object containing only pathi values | Writes pathi value to pathi | | { src1: dest1, src2: dest2 } | Gets new object with value at path srci relocated to desti | Writes srci value to desti |

Chaining

Chaining operations can be a bit confusing. One way to understand it is through seeing how operations distribute.

| Chain | Distributed Chain | | - | - | | [a.b].c | [a.b.c] | | a[b.c] | [a.b.c] | | [a, b].c | [a.c, b.c] | | a[b, c] | [a[c], a[b]] | | {a: b}.c | {a.c: b} | | a{b: c} | {a.b: c} |

Reading .read(source)

An empty string will simply return the original source argument.

Reference

& returns the relative source. For example, "x[&]" will return source.x.

Property

Both .x and [x] can be used to get source.x. They can be chained together via concatenation.

. should only be used for valid variable names.

[ ] can be used for all cases, such at array indices, variable names, quoted strings, and even nested paths.

The following will all get source.a.b.c

a.b.c
[a].b.c
a[b].c
a[b.c]

Array

Array operations will collect values into an array. Shallow operations on this array will have no effect on the source object. You can combine

Consider a case where source = [[1,2],[3,4]]

nrw.parse("").read(source).push(5)        // mutates source
nrw.parse("[]").read(source).push(5)      // doesn't mutate source
nrw.parse("[]").read(source)[0].push(5)   // mutates source
nrw.parse("[][]").read(source)[0].push(5) // doesn't mutate source

| can be used before any array operation to tell it to flatten

nrw.parse("|[]").read(source)  // returns [1,2,3,4]

[begin:end:step] creates a slice using logic similar to the Python slice operation.

[1,5,2] will return [source[1], source[5], source[2]]. A trailing comma is needed to force a single element sequence. For example [0] gets source[0] while [0,] creates [source[0]].

[a.b,x.y] will return [source.a.b, source.x.y]. This also will require tailing comma to force a sequence. If you want to mix array accesses it can be done like so [[0], length] to get [source[0], source.length].

Object

Object operations will collect values into an object. Shallow operations on this object will have no effect on the source object. Mutations should function similar to arrays.

{src: dest} will take do src.read() on the relative source and then dest.write() the result to the current result.

{path} is shorthand for {path: path}.

nrw.parse('{a,b:c}').read({a:1,b:2}) // returns {a:1,c:2}

Writing .write(dest, value)

Write operations function as you might expect once you understand read operations. There are a few caveats specific to write operations, though.

Property

When you write to property that doesn't exist, objects/arrays will be created to ensure you write are setting the property of something other than undefined.

Array

Array operations expect that the value being fed into them is an array.

[] will copy value elements into the array. If the relative destination is large, it will

[@] appends value elements to the end of the array.

[@0] will insert value elements before 0. A negative index relative to the array length can also be given. [@-1] inserts before the last element

Object

{} will do Object.assign() of value into the relative destination.

{src: dest} reads the src path from value and writes it to the dest path of the relative destination.

License

MIT (See LICENSE.md)