Feature request: _.push

[bholben]

When transforming data structures and adding to nested arrays (or creating an array on the fly), we frequently see the following pattern:

if (_.has(o, 'arr')) {
  o.arr.push(val);
} else {
  _.set(o, 'arr', [val]);
}

It would be convenient to replace this with a nice, readable single line. A lodash push method could follow the same signature as _.has, _.get, _.set, and friends:

_.push(o, 'arr', val);

For example, when looping through a data set...

if (_.has(myCalendar.eventsLookup, [userid, dateKey, 'calendarEntries'])) {
  _.get(myCalendar.eventsLookup, [userid, dateKey, 'calendarEntries']).push(calendarEntry);
} else {
  _.set(myCalendar.eventsLookup, [userid, dateKey, 'calendarEntries'], [calendarEntry]);
}

could be simplified to a single line...

_.push(myCalendar.eventsLookup, [userid, dateKey, 'calendarEntries'], calendarEntry);

[jdalton]

I use this pattern in Lodash too though I'm not digging the name push as that seems too Array#push without the object property angle. I think there's something here but think it needs a bit more baking.

Internally I have a castSlice method that performs a slice if it's needed else returns the array without slicing. This method may fit as a cast method.

We'll keep an eye on the popularity of the request.

[bholben]

Yeah, the name may be debatable, but I think the pattern is worthy.

I do like having push in the name as Array#push is the heart of the operation. Casting to an array feels more like a backup plan if the array does not exist. And in this case, I think it's a set that I'm seeking.

Perhaps _.pushSet() might make it more clear that it behaves like Lodash has/set/get (at least that's the signature I have in my head at the moment).

[bholben]

set to me says I'm writing to a plain object, but the underbelly of this is an array operation. The two scenarios I've outlined thus far are either pushing to the back end of the array or unshifting to the front. Maybe something like ensurePush or safePush or pushSafe.

This leaves us some flexibility to expand to other array operations later, whereas I think having set in the name feels limiting in the future.

[jdalton]

Maybe something like ensurePush or safePush or pushSafe.

👍

[mk-pmb]

Here's my first draft of getOrAddKey. Feel free to join me in testing. I'll try and release the lib-demo-util 0.1.8 asap, until then you'll have to stub it somehow or use own tests.

[thorn0]

_.set(o, 'arr[]', val);

Why not make _.set understand such syntax?

It'd be a breaking change though. In the current version this line assigns val to o.arr[""].

[jdalton]

@thorn0 See #1315.

[CongAn]

pushSafe.ts

import { get, set, isArray } from 'lodash'
import { PropertyPath } from 'lodash'

/**
 * 根据object对象的path路径，
 * 安全向数组（不存则会创建该数组）的末尾添加一个或多个元素，并返回新的长度。
 * @author https://github.com/CongAn
 */
export function pushSafe<V>(object: object, path: PropertyPath, ...items: V[]): number
export function pushSafe<V, T extends object>(object: T,  path: PropertyPath, ...items: V[]): number {
    let array = get(object, path)
    if (array === undefined) {
        set(object, path, array = [])
    }
    if (!isArray(array)) {
        throw new Error('The object path of push is not an array.');
    }
    return array.push(...items)
}

export default pushSafe