Clojure's core/get_in in TypeScript

How to use

Install via yarn add locutus and import: import { get_in } from 'locutus/clojure/core/get_in'.

Or with CommonJS: const { get_in } = require('locutus/clojure/core/get_in')

Use a bundler that supports tree-shaking so you only ship the functions you actually use. Vite, webpack, Rollup, and Parcel all handle this. For server-side use this is less of a concern.

Examples

These examples are extracted from test cases that automatically verify our functions against their native counterparts.

#	code	expected result
1	get_in({a: {b: 42}}, ['a', 'b'])	42
2	get_in({a: {b: 42}}, ['a', 'c'], 'fallback')	'fallback'
3	get_in([10, {x: [1, 2, 3]}], [1, 'x', 2], null)	3

Notes

• Reads nested values by path, similar to Clojure get-in.

Here's what our current TypeScript equivalent to Clojure's core/get_in looks like.

TSTypeScript JSJavaScript TSStandalone TS JSStandalone JS

Copy code

type PathKey = string | number

function readAtPath(target: unknown, key: PathKey): unknown {
  if (target === null || target === undefined) {
    return undefined
  }

  if (typeof target !== 'object') {
    return undefined
  }

  return (target as Record<string | number, unknown>)[key]
}

export function get_in(value: unknown, keys: PathKey[] | unknown): unknown
export function get_in(value: unknown, keys: PathKey[] | unknown, defaultValue: unknown): unknown
export function get_in(value: unknown, keys: PathKey[] | unknown, defaultValue?: unknown): unknown {
  //  discuss at: https://locutus.io/clojure/get_in/
  // original by: Kevin van Zonneveld (https://kvz.io)
  //      note 1: Reads nested values by path, similar to Clojure get-in.
  //   example 1: get_in({a: {b: 42}}, ['a', 'b'])
  //   returns 1: 42
  //   example 2: get_in({a: {b: 42}}, ['a', 'c'], 'fallback')
  //   returns 2: 'fallback'
  //   example 3: get_in([10, {x: [1, 2, 3]}], [1, 'x', 2], null)
  //   returns 3: 3

  if (!Array.isArray(keys)) {
    return defaultValue
  }

  if (keys.length === 0) {
    return value
  }

  let cursor: unknown = value
  for (const key of keys) {
    cursor = readAtPath(cursor, key)
    if (cursor === undefined) {
      return defaultValue
    }
  }

  return cursor
}

function readAtPath(target, key) {
  if (target === null || target === undefined) {
    return undefined
  }

  if (typeof target !== 'object') {
    return undefined
  }

  return target[key]
}
export function get_in(value, keys, defaultValue) {
  //  discuss at: https://locutus.io/clojure/get_in/
  // original by: Kevin van Zonneveld (https://kvz.io)
  //      note 1: Reads nested values by path, similar to Clojure get-in.
  //   example 1: get_in({a: {b: 42}}, ['a', 'b'])
  //   returns 1: 42
  //   example 2: get_in({a: {b: 42}}, ['a', 'c'], 'fallback')
  //   returns 2: 'fallback'
  //   example 3: get_in([10, {x: [1, 2, 3]}], [1, 'x', 2], null)
  //   returns 3: 3

  if (!Array.isArray(keys)) {
    return defaultValue
  }

  if (keys.length === 0) {
    return value
  }

  let cursor = value
  for (const key of keys) {
    cursor = readAtPath(cursor, key)
    if (cursor === undefined) {
      return defaultValue
    }
  }

  return cursor
}

Improve this function

Locutus is a community effort following The McDonald's Theory: we ship first iterations, hoping others will improve them. If you see something that could be better, we'd love your contribution.

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