object-scan

Object-Scan

Find keys in object hierarchies using wildcard and glob matching and callbacks.

Install

Install with npm:

$ npm install --save object-scan

Usage

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

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

Features

• Input traversed exactly once during search
• Dependency free, small in size and very performant
• Object and Array matching with e.g. key.path and [1]
• Wildcard matching with * and [*]
• Partial Wildcard matching with e.g. mark*, m?rk, [*1] or [?1]
• Arbitrary depth matching with **
• Or-clause with e.g. {a,b} and [{0,1}]
• Exclusion with e.g. !key
• Full support for escaping
• Results returned in "delete-safe" order
• Search syntax is checked for correctness
• Lots of tests to ensure correctness

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.

Options

Signature of all callbacks is

Fn({
  key, value, parent, parents, isMatch, matchedBy, excludedBy, traversedBy, isCircular
  getKey, getValue, getParent, getParents, getIsMatch, getMatchedBy, getExcludedBy, getTraversedBy, getIsCircular
  context
})

where:

• key: key that callback is invoked for (respects joined option).
• value: value for key.
• 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
• getKey: function that returns key
• getValue: function that returns value
• 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
• 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

If 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().

breakFn

Type: function
Default: undefined

If 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.

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.

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.

strict

Type: boolean
Default: true

When set to false, no errors are thrown when:

• the input contains redundant needles

Examples

More extensive examples can be found in the tests.

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

const obj = {
  a: {
    b: {
      c: 'd'
    },
    e: {
      f: 'g'
    },
    h: ['i', 'j']
  },
  k: 'l'
};

// top level keys
objectScan(['*'], { joined: true })(obj);
// => ["k", "a"]

// nested keys
objectScan(['a.*.f'], { joined: true })(obj);
// => ["a.e.f"]
objectScan(['*.*.*'], { joined: true })(obj);
// => ["a.e.f", "a.b.c"]

// or filter
objectScan(['a.*.{c,f}'], { joined: true })(obj);
// => ["a.e.f", "a.b.c"]
objectScan(['a.*.{c,f}'])(obj);
// => [["a", "e", "f"], ["a", "b", "c"]]

// list filter
objectScan(['*.*[*]'], { joined: true })(obj);
// => ["a.h[1]", "a.h[0]"]
objectScan(['*[*]'], { joined: true })(obj);
// => []

// deep star filter
objectScan(['**'], { joined: true })(obj);
// => ["k", "a.h[1]", "a.h[0]", "a.h", "a.e.f", "a.e", "a.b.c", "a.b", "a"]
objectScan(['**.f'], { joined: true })(obj);
// => ["a.e.f"]
objectScan(['**[*]'], { joined: true })(obj);
// => ["a.h[1]", "a.h[0]"]

// exclusion filter
objectScan(['a.*,!a.e'], { joined: true })(obj);
// => ["a.h", "a.b"]

// value function
objectScan(['**'], { filterFn: ({ value }) => typeof value === 'string', joined: true })(obj);
// => ["k", "a.h[1]", "a.h[0]", "a.e.f", "a.b.c"]
objectScan(['**'], { breakFn: ({ key }) => key === 'a.b', joined: true })(obj);
// => ["k", "a.h[1]", "a.h[0]", "a.h", "a.e.f", "a.e", "a.b", "a"]

Edge Cases

The top level object(s) are matched by the empty needle "". Useful for matching objects nested in arrays by setting useArraySelector to false. Note that the empty string does not work with _.get and _.set.

Special Characters

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

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.