javascript recursive function concat not working

Question

I have a nested array of objects like below and I'm trying to push all the values in to a single array. all the values are located in sp->it->value or sp->it->it->value

[
{
    "sp": [
            {
              "it":[
                    {"value":5}
               ]
            },
            ...
        ],
    "b": {
        ...
    }
},
{
    "sp": [
            {
              "it":[
                {"nm":5}
                ]
            }
        ],
    "b": {
        ...
    }
},
{
    "sp": [
            {
              "it":[
                {
                  "it":[
                    {"value":5}
                  ]
                }
               ]
           }
        ],
    "b": {
        ...
    }
},

]

and here is what I have tried

const getValues = (js) => {
    let values = []
    js.map((val,i) => {
        if("sp" in val) values.concat(getValues(val.sp))
        else if("it" in val) values.concat(getValues(val.it))
         else if("value" in val) values.push(val.value)
    })
    return values
}

I thought I could concatenate the returned value from the recursive call since it returns an array but the above code returns empty array. Any insights?

Edit fixed the typo on sp object. It is array of objects.

map returns an array. If you're not going to use the return value, use forEach. — Heretic Monkey
– Heretic Monkey, Commented Aug 28, 2019 at 18:13
You didn't fix anything related to my comment. You're still using map for side effects instead of using it for its return value. — Heretic Monkey
– Heretic Monkey, Commented Aug 28, 2019 at 18:20

t.niese · Accepted Answer · 2019-08-28 18:17:02Z

1

Array.prototype.concat()

The concat() method is used to merge two or more arrays. This method does not change the existing arrays, but instead returns a new array.

So those lines do nothing:

if("sp" in val) values.concat(getValues(val.sp))
else if("it" in val) values.concat(getValues(val.it))

You need to write:

if("sp" in val) values = values.concat(getValues(val.sp))
else if("it" in val) values = values.concat(getValues(val.it))

And you should not use map if you don't use it's result. Use forEach instead.

answered Aug 28, 2019 at 18:17

t.niese

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Rahul Beniwal · Accepted Answer · 2019-08-28 18:11:42Z

1

This is because you are passing val.sp to function which is not array but it is an object and .map is a property of an array

answered Aug 28, 2019 at 18:11

Rahul Beniwal

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