object-scan

Object-Scan

Find keys in object hierarchies using wildcard 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

• 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
• Input traversed exactly once during search
• Results returned in "delete-safe" order
• Search syntax is checked for correctness
• Dependency free, small in size and very performant
• Lots of tests to ensure correctness

Options

Signature for all functions is

Fn(key, value, { parents, isMatch, matchedBy, excludedBy, traversedBy })

where:

• key is the key that the function is called for (respects joined option).
• value is the value for that key.
• parents is array of form [parent, grandparent, ...].
• isMatch is true if the last targeting needle exists and is non-excluding.
• matchedBy are all non-excluding needles targeting the key.
• excludedBy are all excluding needles targeting the key.
• traversedBy are all needles involved in traversing the key.

filterFn

Type: function
Default: undefined

If function is defined, it is called for every match. If false is returned, the current key is excluded from the result.

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

Called in same order as matches would appear in result.

This method is conceptually similar to the callback function in Array.filter().

breakFn

Type: function
Default: undefined

If function is defined, it is called 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 called before the corresponding filterFn might be called.

joined

Type: boolean
Default: true

Can be set to false to return each key as a list. When dealing with special characters this can be useful.

Setting this to false improves 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(['*'])(obj);
// => ["k", "a"]

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

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

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

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

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

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

When dealing with special characters, it might be desirable to set the joined option to false.

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 called, 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.