Skip to main content

Recurse JavaScript Object to Get Values for a Given Key the Easy Way

· 2 min read
Jeffrey Aven

I had a scenario where I needed to find values for a key in a complex JavaScript object which could be nested n levels deep.

I found numerous approaches to doing this, most were overly complicated, so I thought I would share the most straightforward, concise process.

the Code

You can do this in a straightforward function implementing the "tail call recursion" pattern to search for a key (key) from the root of an object (obj), excluding any keys in excludeKeys.

This will return a list of values for the given key, searching all levels in all branches of the object.

function getAllValuesForKey(obj, key, excludeKeys=[], values=[]) {
for (let k in obj) {
if (typeof obj[k] === "object") {
if(!excludeKeys.includes(k)){
getAllValuesForKey(obj[k], key, excludeKeys, values)
}
} else {
if (k === key){
values.push(obj[k]);
}
}
}
return values;
}

Example

In parsing an OpenAPI or Swagger specification, I am looking for all of the schema refs in a successful response body, for example:

paths:
'/orgs/{org}/actions/permissions/selected-actions':
get:
...
responses:
'200': '...'

however these refs can present in various different ways depending upon the response type, such as:

'200':
$ref: '#/components/responses/actions_runner_labels'

or

'200':      
content:
application/json:
schema:
$ref: '#/components/schemas/runner'

or

'200':
content:
application/json:
schema:
anyOf:
- $ref: '#/components/schemas/interaction-limit-response'

or

'200':
content:
application/json:
schema:
type: object
required:
- total_count
- runners
properties:
total_count:
type: integer
runners:
type: array
items:
$ref: '#/components/schemas/runner'

To find all of the schema refs without knowing the response type or structure I used the above function as follows (excluding refs for examples):

function getRespSchemaName(op){
for(let respCode in op.responses){
if(respCode.startsWith('2')){
return getAllValuesForKey(op.responses[respCode], "$ref", ['examples']);
}
}
}

You can find this implementation in openapi-doc-util and @stackql/openapi-doc-util.

simple!