How to add multiple arrays to object in function return?

Question

I have a function that takes in an object as a prop and needs to add arrays to it using a for loop. My problem is that it only works if a single array is added when it is called. If more than one array is to be added, I receive the error linkLineItems.push is not a function, but I thought .push could be used to add arrays to objects.

Here is the function:

function PrepareSuccessorActivityLinkData(data, existingLinks, linkSetter) {
  for (let [key, value] of Object.entries(data)) {
    let linkLineItems;
    let linkLineItem;
    if (data.activitiesafter[0] != "DEFAULT") {
      for (var i = 0; i < data.activitiesafter.length; i++) {
        linkLineItem = {
          source: data.itemname,
          target: data.activitiesafter[i],
          type: "activity-activity-after"
        };
        if (!linkLineItems) {
          linkLineItems = linkLineItem;
        } else {
          linkLineItems.push(linkLineItem);
        }
      }
    } else {
      continue;
    }
    return linkSetter(linkData => [...existingLinks, linkLineItems]);
  }
}

Any help on how to add multiple arrays to an object?

Edit #1: Sample data for the existingLinks or object that I'm trying to add items to

var linksData = [
 {"source": "Do Something", "target": "My Document", "type": "Activity Output"},
 {"source": "My Document", "target": "Operator", "type": "Object Responsible"},
 {"source": "Operator", "target": "Do Something", "type": "Role Activity"}
];

Edit #2: Sample data that's being passed into the function as data

[{
 itemname: "Hello World", 
 itemtype: "activity", 
 activitiesafter: ["Do Stuff", "Do Other Stuff"]
}]

You can't push onto an object. Set a property instead linkLineItems.something = [] — evolutionxbox
– evolutionxbox, Commented Apr 5, 2020 at 20:45
push can only be used on Arrays. It would be helpful if you add some example input/output data. It's a little difficult to tell exactly what your desired behavior is here — schu34
– schu34, Commented Apr 5, 2020 at 20:46
@schu34 I added sample data. The function needs to be able to add more than one array at a time (based on the activitiesafter for loop. — userNick
– userNick, Commented Apr 5, 2020 at 20:55
@usernick I am not discussing your problem, I am stating that calling linkSetter and so on is not what you have trouble with. The difficulty you encounter is just to build linkLineItems out of data passed as argument. All the context is not that useful. The two things which matter (and that we miss) are the content of data (if need be console.log(JSON.stringify(data)) and the expected linkLineItems which should be constructed — grodzi
– grodzi, Commented Apr 6, 2020 at 12:34
@grodzi I added edit #2 to the main post to show the data being passed into the function — userNick
– userNick, Commented Apr 6, 2020 at 13:46

grodzi · Accepted Answer · 2020-04-06 19:03:53Z

1

Some self proclaimed best practices:

Avoid if possible for-loops when you don't need indices. (see forEach and alike). This allows less variables which pollute your eyes.
Make early "continue" or "return" to avoid nesting stuff (e.g return links comes first)
Try to reduce at max the scope of your variables. This is also achieved here by using forEach

function nameTooLong(data, existingLinks, linkSetter) {
  const moreLinks = data.reduce((links, item) => {
    if (item.activitiesafter[0] === "DEFAULT") {
      return links
    }
    item.activitiesafter.forEach(activity => {
      links.push({
        source: item.itemname,
        target: activity,
        type: "activity-activity-after"
      })
    })
    return links
  }, [])
  return linkSetter(_ => existingLinks.concat(moreLinks))
}

nameTooLong([{
 itemname: "Hello World", 
 itemtype: "activity", 
 activitiesafter: ["Do Stuff", "Do Other Stuff"]
},{
 itemname: "shold be ignored", 
 itemtype: "activity", 
 activitiesafter: ["DEFAULT", "nothing there"]
}], ['toto'], (fn) => console.log('newlinks: ', fn()))

If you read 3., we can do better and even avoid manipulating the variable links by using flatMap

function nameTooLong(data, existingLinks, linkSetter) {
  const moreLinks = data.flatMap(item => {
    if (item.activitiesafter[0] === "DEFAULT") {
      return []
    }
    return item.activitiesafter.map(activity => ({
      source: item.itemname,
      target: activity,
      type: "activity-activity-after"
    }))
  })
  return linkSetter(_ => existingLinks.concat(moreLinks))
}

nameTooLong([{
 itemname: "Hello World", 
 itemtype: "activity", 
 activitiesafter: ["Do Stuff", "Do Other Stuff"]
},{
 itemname: "shold be ignored", 
 itemtype: "activity", 
 activitiesafter: ["DEFAULT", "nothing there"]
}], ['toto'], (fn) => console.log('newlinks: ', fn()))

answered Apr 6, 2020 at 19:03

grodzi

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3 Comments

userNick Over a year ago

This is awesome, I didn't know about flatMap. However, I'm getting the error data.flatMap is not a function when plugging the function into my app. It's weird because I can console.log(data), store it as a variable in the console, and data.flatMap works there. Any ideas?

userNick Over a year ago

Answering my own question from my last comment. I got it to work if I instantiated the array by wrapping data in [ ]. So the function starts with const moreLinks = [data].flatMap(item => {

grodzi Over a year ago

@userNick if data is not an array (in your real work case), then you don't need to iterate over data, just process the plain object!

Owl Surojit · Accepted Answer · 2020-04-05 21:09:19Z

0

The push function only works on arrays, not on objects.

And since I don't see any reason linkLineItems needs to be an object I would suggest you just make it an array by initialising it with let linkLineItems = [];.

answered Apr 5, 2020 at 21:09

Owl Surojit

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1 Comment

userNick Over a year ago

I made some updates to the original post to provide more context, but initializing the array with [ ] does not seem to result in the desired result of adding multiple arrays to a parent object.

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