object-scan

Object-Scan

Traverse object hierarchies using matching and callbacks.

Install

Install with npm:

$ npm install --save object-scan

Usage

const objectScan = require('object-scan');

const haystack = { a: { b: { c: 'd' }, e: { f: 'g' } } };
objectScan(['a.*.f'], { joined: true })(haystack);
// => [ 'a.e.f' ]

Features

• Input traversed exactly once during search
• Dependency free, small in size and very performant
• Separate Object and Array matching
• Wildcard and Regex matching
• Arbitrary depth matching
• Or-clause Syntax
• Exclusion Matching
• Full support for escaping
• Traversal in "delete-safe" order
• Recursion free implementation
• Search syntax validated
• Lots of tests and examples

Matching

A needle expression specifies one or more paths to an element (or a set of elements) in a JSON structure. Paths use the dot notation:

store.book[0].title

Array

Rectangular brackets for array path matching.

Examples:

['[2]'] (exact in array)

const haystack = [0, 1, 2, 3, 4];
objectScan(['[2]'], { joined: true })(haystack);
// => [ '[2]' ]

['[1]'] (no match in object)

const haystack = { 0: 'a', 1: 'b', 2: 'c' };
objectScan(['[1]'], { joined: true })(haystack);
// => []

Object

Property name for object property matching.

Examples:

['foo'] (exact in object)

const haystack = { foo: 0, bar: 1 };
objectScan(['foo'], { joined: true })(haystack);
// => [ 'foo' ]

['1'] (no match in array)

const haystack = [0, 1, 2, 3, 4];
objectScan(['1'], { joined: true })(haystack);
// => []

Wildcard

The following characters have special meaning when not escaped:

• *: Match zero or more character
• +: Match one or more character
• ?: Match exactly one character
• \: Escape the subsequent character

Wildcards can be used with Array and Object selector.

Examples:

['*'] (top level)

const haystack = { a: { b: 0, c: 1 }, d: 2 };
objectScan(['*'], { joined: true })(haystack);
// => [ 'd', 'a' ]

['[?5]'] (two digit ending in five)

const haystack = [...Array(30).keys()];
objectScan(['[?5]'], { joined: true })(haystack);
// => [ '[25]', '[15]' ]

['a.+.c'] (nested)

const haystack = { a: { b: { c: 0 }, d: { f: 0 } } };
objectScan(['a.+.c'], { joined: true })(haystack);
// => [ 'a.b.c' ]

['a.\\+.c'] (escaped)

const haystack = { a: { b: { c: 0 }, '+': { c: 0 } } };
objectScan(['a.\\+.c'], { joined: true })(haystack);
// => [ 'a.\\+.c' ]

Regex

Regex are defined by using parentheses.

Can be used with Array and Object selector.

Examples:

['(^foo)'] (starting with `foo`)

const haystack = { foo: 0, foobar: 1, bar: 2 };
objectScan(['(^foo)'], { joined: true })(haystack);
// => [ 'foobar', 'foo' ]

['[(5)]'] (containing `5`)

const haystack = [...Array(20).keys()];
objectScan(['[(5)]'], { joined: true })(haystack);
// => [ '[15]', '[5]' ]

['[(^[01]$)]'] (`[0]` and `[1]`)

const haystack = ['a', 'b', 'c', 'd'];
objectScan(['[(^[01]$)]'], { joined: true })(haystack);
// => [ '[1]', '[0]' ]

['[(^[^01]$)]'] (other than `[0]` and `[1]`)

const haystack = ['a', 'b', 'c', 'd'];
objectScan(['[(^[^01]$)]'], { joined: true })(haystack);
// => [ '[3]', '[2]' ]

['[*]', '[!(^[01]$)]'] (match all and exclude `[0]` and `[1]`)

const haystack = ['a', 'b', 'c', 'd'];
objectScan(['[*]', '[!(^[01]$)]'], { joined: true })(haystack);
// => [ '[3]', '[2]' ]

Arbitrary Depth

There are two types of arbitrary depth matching:

• **: Matches zero or more nestings
• ++: Matches one or more nestings

Recursions can be combined with a regex by appending the regex.

Examples:

['a.**'] (zero or more nestings under `a`)

const haystack = { a: { b: 0, c: 0 } };
objectScan(['a.**'], { joined: true })(haystack);
// => [ 'a.c', 'a.b', 'a' ]

['a.++'] (one or more nestings under `a`)

const haystack = { a: { b: 0, c: 0 } };
objectScan(['a.++'], { joined: true })(haystack);
// => [ 'a.c', 'a.b' ]

['**(1)'] (all containing `1` at every level)

const haystack = { 1: { 1: ['c', 'd'] }, 510: 'e', foo: { 1: 'f' } };
objectScan(['**(1)'], { joined: true })(haystack);
// => [ '510', '1.1[1]', '1.1', '1' ]

Or Clause

Or Clauses are defined by using curley brackets.

Can be used with Array and Object selector.

Examples:

['[{0,1}]'] (`[0]` and `[1]`)

const haystack = ['a', 'b', 'c', 'd'];
objectScan(['[{0,1}]'], { joined: true })(haystack);
// => [ '[1]', '[0]' ]

['{a,d}.{b,f}'] (`a.b`, `a.f`, `d.b` and `d.f`)

const haystack = { a: { b: 0, c: 1 }, d: { e: 2, f: 3 } };
objectScan(['{a,d}.{b,f}'], { joined: true })(haystack);
// => [ 'd.f', 'a.b' ]

Exclusion

To exclude a path, use exclamation mark.

Examples:

['{a,b},!a'] (only `b`)

const haystack = { a: 0, b: 1 };
objectScan(['{a,b},!a'], {
  joined: true,
  strict: false
})(haystack);
// => [ 'b' ]

['**,!**.a'] (all except ending in `a`)

const haystack = { a: 0, b: { a: 1, c: 2 } };
objectScan(['**,!**.a'], { joined: true })(haystack);
// => [ 'b.c', 'b' ]

Escaping

The following characters are considered special and need to be escaped using \, if they should be matched in a key:
[, ], {, }, (, ), ,, ., !, ?, *, + and \.

Examples:

['\\[1\\]'] (special object key)

const haystack = { '[1]': 0 };
objectScan(['\\[1\\]'], { joined: true })(haystack);
// => [ '\\[1\\]' ]

Options

Signature of all callbacks is

Fn({ key, value, ... })

where:

• key: key that callback is invoked for (respects joined option).
• value: value for key.
• entry: entry consisting of [key, value].
• property: current parent property.
• parent: current parent.
• parents: array of form [parent, grandparent, ...].
• isMatch: true iff last targeting needle exists and is non-excluding.
• matchedBy: all non-excluding needles targeting key.
• excludedBy: all excluding needles targeting key.
• traversedBy: all needles involved in traversing key.
• isCircular: true iff value contained in parents
• isLeaf: true iff value can not be traversed
• getKey: function that returns key
• getValue: function that returns value
• getEntry: function that returns entry
• getProperty: function that returns property
• getParent: function that returns parent
• getParents: function that returns parents
• getIsMatch: function that returns isMatch
• getMatchedBy: function that returns matchedBy
• getExcludedBy: function that returns excludedBy
• getTraversedBy: function that returns traversedBy
• getIsCircular: function that returns isCircular
• getIsLeaf: function that returns isLeaf
• context: as passed into the search

Notes on Performance:

• Arguments backed by getters use Functions Getter and should be accessed via destructuring to prevent redundant computation.
• Getters should be used to improve performance for conditional access. E.g. if (isMatch) { getParents() ... }.
• For performance reasons, the same object is passed to all callbacks.

filterFn

Type: function
Default: undefined

When defined, this callback is invoked for every match. If false is returned, the current key is excluded from the result.

The return value of this callback has no effect when a search context is provided.

Can be used to do processing as matching keys are traversed.

Invoked in same order as matches would appear in result.

This method is conceptually similar to Array.filter().

Examples:

['**'] (filter function)

const haystack = { a: 0, b: 'bar' };
objectScan(['**'], {
  joined: true,
  filterFn: ({ value }) => typeof value === 'string'
})(haystack);
// => [ 'b' ]

breakFn

Type: function
Default: undefined

When defined, this callback is invoked for every key that is traversed by the search. If true is returned, all keys nested under the current key are skipped in the search and from the final result.

Note that breakFn is invoked before the corresponding filterFn might be invoked.

Examples:

['**'] (break function)

const haystack = { a: { b: { c: 0 } } };
objectScan(['**'], {
  joined: true,
  breakFn: ({ key }) => key === 'a.b'
})(haystack);
// => [ 'a.b', 'a' ]

compareFn

Type: function
Default: undefined

When defined, this function is used as a comparator to determine the traversal order of any object keys.

This works together with the reverse option.

Examples:

['**'] (simple sort)

const haystack = { a: 0, c: 1, b: 2 };
objectScan(['**'], {
  joined: true,
  compareFn: (k1, k2) => k1.localeCompare(k2),
  reverse: false
})(haystack);
// => [ 'a', 'b', 'c' ]

reverse

Type: boolean
Default: true

When set to true, the scan is performed in reverse order. This means breakFn is executed in reverse post-order and filterFn in reverse pre-order. Otherwise breakFn is executed in pre-order and filterFn in post-order.

When reverse is true the scan is delete-safe. I.e. property can be deleted / spliced from parent object / array in filterFn.

Examples:

['**'] (breakFn, reverse true)

const haystack = { f: { b: { a: {}, d: { c: {}, e: {} } }, g: { i: { h: {} } } } };
objectScan(['**'], {
  breakFn: ({ isMatch, property, context }) => { if (isMatch) { context.push(property); } },
  reverse: true
})(haystack, []);
// => [ 'f', 'g', 'i', 'h', 'b', 'd', 'e', 'c', 'a' ]

['**'] (filterFn, reverse true)

const haystack = { f: { b: { a: {}, d: { c: {}, e: {} } }, g: { i: { h: {} } } } };
objectScan(['**'], {
  filterFn: ({ property, context }) => { context.push(property); },
  reverse: true
})(haystack, []);
// => [ 'h', 'i', 'g', 'e', 'c', 'd', 'a', 'b', 'f' ]

['**'] (breakFn, reverse false)

const haystack = { f: { b: { a: {}, d: { c: {}, e: {} } }, g: { i: { h: {} } } } };
objectScan(['**'], {
  breakFn: ({ isMatch, property, context }) => { if (isMatch) { context.push(property); } },
  reverse: false
})(haystack, []);
// => [ 'f', 'b', 'a', 'd', 'c', 'e', 'g', 'i', 'h' ]

['**'] (filterFn, reverse false)

const haystack = { f: { b: { a: {}, d: { c: {}, e: {} } }, g: { i: { h: {} } } } };
objectScan(['**'], {
  filterFn: ({ property, context }) => { context.push(property); },
  reverse: false
})(haystack, []);
// => [ 'a', 'c', 'e', 'd', 'b', 'h', 'i', 'g', 'f' ]

abort

Type: boolean
Default: false

When set to true the scan immediately returns after the first match.

Examples:

['a', 'b'] (only return first property)

const haystack = { a: 0, b: 1 };
objectScan(['a', 'b'], {
  rtn: 'property',
  abort: true
})(haystack);
// => 'b'

['[0]', '[1]'] (abort changes count)

const haystack = ['a', 'b'];
objectScan(['[0]', '[1]'], {
  rtn: 'count',
  abort: true
})(haystack);
// => 1

rtn

Type: string
Default: dynamic

Defaults to key when search context is undefined and to context otherwise.

Can be explicitly set as:

• context: search context is returned
• key: matched keys are returned
• value: matched values are returned
• entry: matched entries are returned
• property: matched properties are returned
• parent: matched parent are returned
• parents: matched parents are returned
• bool: returns true iff a match is found
• count: returns the match count

When abort is set to true and the result would be a list, the first match or undefined is returned.

Examples:

['[*]'] (return values)

const haystack = ['a', 'b', 'c'];
objectScan(['[*]'], { rtn: 'value' })(haystack);
// => [ 'c', 'b', 'a' ]

['foo[*]'] (return entries)

const haystack = { foo: ['bar'] };
objectScan(['foo[*]'], { rtn: 'entry' })(haystack);
// => [ [ [ 'foo', 0 ], 'bar' ] ]

['a.b.c', 'a'] (return properties)

const haystack = { a: { b: { c: 0 } } };
objectScan(['a.b.c', 'a'], { rtn: 'property' })(haystack);
// => [ 'c', 'a' ]

['a.b', 'a.c'] (checks for any match, full scan)

const haystack = { a: { b: 0, c: 1 } };
objectScan(['a.b', 'a.c'], { rtn: 'bool' })(haystack);
// => true

['**'] (return not provided context)

const haystack = { a: 0 };
objectScan(['**'], { rtn: 'context' })(haystack);
// => undefined

['a.b.{c,d}'] (return keys with context passed)

const haystack = { a: { b: { c: 0, d: 1 } } };
objectScan(['a.b.{c,d}'], { rtn: 'key' })(haystack, []);
// => [ [ 'a', 'b', 'd' ], [ 'a', 'b', 'c' ] ]

joined

Type: boolean
Default: false

Keys are returned as a string when set to true instead of as a list.

Setting this option to true will negatively impact performance.

Note that _.get and _.set fully support lists.

Examples:

['[*]', '[*].foo'] (joined)

const haystack = [0, 1, { foo: 'bar' }];
objectScan(['[*]', '[*].foo'], { joined: true })(haystack);
// => [ '[2].foo', '[2]', '[1]', '[0]' ]

['[*]', '[*].foo'] (not joined)

const haystack = [0, 1, { foo: 'bar' }];
objectScan(['[*]', '[*].foo'])(haystack);
// => [ [ 2, 'foo' ], [ 2 ], [ 1 ], [ 0 ] ]

useArraySelector

Type: boolean
Default: true

When set to false, no array selectors should be used in any needles and arrays are automatically traversed.

Note that the results still include the array selectors.

Examples:

['a', 'b.d'] (automatic array traversal)

const haystack = [{ a: 0 }, { b: [{ c: 1 }, { d: 2 }] }];
objectScan(['a', 'b.d'], {
  joined: true,
  useArraySelector: false
})(haystack);
// => [ '[1].b[1].d', '[0].a' ]

[''] (top level array matching)

const haystack = [{ a: 0 }, { b: 1 }];
objectScan([''], {
  joined: true,
  useArraySelector: false
})(haystack);
// => [ '[1]', '[0]' ]

strict

Type: boolean
Default: true

When set to true, errors are thrown when:

• a path is identical to a previous path
• a path invalidates a previous path
• a path contains consecutive recursions

Examples:

['a.b', 'a.b'] (identical)

const haystack = [];
objectScan(['a.b', 'a.b'], { joined: true })(haystack);
// => 'Error: Redundant Needle Target: "a.b" vs "a.b"'

['a.{b,b}'] (identical, same needle)

const haystack = [];
objectScan(['a.{b,b}'], { joined: true })(haystack);
// => 'Error: Redundant Needle Target: "a.{b,b}" vs "a.{b,b}"'

['a.b', 'a.**'] (invalidates previous)

const haystack = [];
objectScan(['a.b', 'a.**'], { joined: true })(haystack);
// => 'Error: Needle Target Invalidated: "a.b" by "a.**"'

['**.!**'] (consecutive recursion)

const haystack = [];
objectScan(['**.!**'], { joined: true })(haystack);
// => 'Error: Redundant Recursion: "**.!**"'

Search Context

A context can be passed into a search invocation as a second parameter. It is available in all callbacks and can be used to manage state across a search invocation without having to recompile the search.

By default all matched keys are returned from a search invocation. However, when it is not undefined, the context is returned instead.

Examples:

['**.{c,d,e}'] (sum values)

const haystack = { a: { b: { c: 2, d: 11 }, e: 7 } };
objectScan(['**.{c,d,e}'], {
  joined: true,
  filterFn: ({ value, context }) => { context.sum += value; }
})(haystack, { sum: 0 });
// => { sum: 20 }

Examples

More extensive examples can be found in the tests.

['a.*.f'] (nested)

const haystack = { a: { b: { c: 'd' }, e: { f: 'g' }, h: ['i', 'j'] }, k: 'l' };
objectScan(['a.*.f'], { joined: true })(haystack);
// => [ 'a.e.f' ]

['*.*.*'] (multiple nested)

const haystack = { a: { b: { c: 'd' }, e: { f: 'g' }, h: ['i', 'j'] }, k: 'l' };
objectScan(['*.*.*'], { joined: true })(haystack);
// => [ 'a.e.f', 'a.b.c' ]

['a.*.{c,f}'] (or filter)

const haystack = { a: { b: { c: 'd' }, e: { f: 'g' }, h: ['i', 'j'] }, k: 'l' };
objectScan(['a.*.{c,f}'], { joined: true })(haystack);
// => [ 'a.e.f', 'a.b.c' ]

['a.*.{c,f}'] (or filter, not joined)

const haystack = { a: { b: { c: 'd' }, e: { f: 'g' }, h: ['i', 'j'] }, k: 'l' };
objectScan(['a.*.{c,f}'])(haystack);
// => [ [ 'a', 'e', 'f' ], [ 'a', 'b', 'c' ] ]

['*.*[*]'] (list filter)

const haystack = { a: { b: { c: 'd' }, e: { f: 'g' }, h: ['i', 'j'] }, k: 'l' };
objectScan(['*.*[*]'], { joined: true })(haystack);
// => [ 'a.h[1]', 'a.h[0]' ]

['*[*]'] (list filter, unmatched)

const haystack = { a: { b: { c: 'd' }, e: { f: 'g' }, h: ['i', 'j'] }, k: 'l' };
objectScan(['*[*]'], { joined: true })(haystack);
// => []

['**'] (star recursion)

const haystack = { a: { b: { c: 'd' }, e: { f: 'g' }, h: ['i', 'j'] }, k: 'l' };
objectScan(['**'], { joined: true })(haystack);
// => [ 'k', 'a.h[1]', 'a.h[0]', 'a.h', 'a.e.f', 'a.e', 'a.b.c', 'a.b', 'a' ]

['++.++'] (plus recursion)

const haystack = { a: { b: { c: 'd' }, e: { f: 'g' }, h: ['i', 'j'] }, k: 'l' };
objectScan(['++.++'], { joined: true })(haystack);
// => [ 'a.h[1]', 'a.h[0]', 'a.h', 'a.e.f', 'a.e', 'a.b.c', 'a.b' ]

['**.f'] (star recursion ending in f)

const haystack = { a: { b: { c: 'd' }, e: { f: 'g' }, h: ['i', 'j'] }, k: 'l' };
objectScan(['**.f'], { joined: true })(haystack);
// => [ 'a.e.f' ]

['**[*]'] (star recursion ending in array)

const haystack = { a: { b: { c: 'd' }, e: { f: 'g' }, h: ['i', 'j'] }, k: 'l' };
objectScan(['**[*]'], { joined: true })(haystack);
// => [ 'a.h[1]', 'a.h[0]' ]

['a.*,!a.e'] (exclusion filter)

const haystack = { a: { b: { c: 'd' }, e: { f: 'g' }, h: ['i', 'j'] }, k: 'l' };
objectScan(['a.*,!a.e'], { joined: true })(haystack);
// => [ 'a.h', 'a.b' ]

['**.(^[bc]$)'] (regex matching)

const haystack = { a: { b: { c: 'd' }, e: { f: 'g' }, h: ['i', 'j'] }, k: 'l' };
objectScan(['**.(^[bc]$)'], { joined: true })(haystack);
// => [ 'a.b.c', 'a.b' ]

Edge Cases

Top level object(s) are matched by the empty needle ''. This is useful for matching objects nested in arrays by setting useArraySelector to false. To match the actual empty string as a key, use (^$).

Note that the empty string does not work to match top level objects with _.get or _.set.

Examples:

[''] (match top level objects in array)

const haystack = [{}, {}];
objectScan([''], {
  joined: true,
  useArraySelector: false
})(haystack);
// => [ '[1]', '[0]' ]

[''] (match top level object)

const haystack = {};
objectScan([''], { joined: true })(haystack);
// => [ '' ]

['**.(^$)'] (match empty string keys)

const haystack = { '': 0, a: { '': 1 } };
objectScan(['**.(^$)'])(haystack);
// => [ [ 'a', '' ], [ '' ] ]

Internals

Conceptually this package works as follows:

1. During initialization the needles are parsed and built into a search tree. Various information is pre-computed and stored for every node. Finally the search function is returned.

2. When the search function is invoked, the input is traversed simultaneously with the relevant nodes of the search tree. Processing multiple search tree branches in parallel allows for a single traversal of the input.

Having a separate initialization stage allows for a performant search and significant speed ups when applying the same search to different input.