Don't understand objects

JavaScript
#1

Hi folks, i want to iterate over array of objects and rename two keys, i want to keep others as they are.

here is my code:

    const translated = trimmed.map((obj) => {
      return { typ: obj.objType, name: obj.caption}
    })

This returns object with only typ and name, all other values are deleted .
why is that ?

#2

The trim() method removes whitespace from both ends of a string. Whitespace in this context is all the whitespace characters (space, tab, no-break space, etc.) and all the line terminator characters (LF, CR, etc.).

#3

i don’t use trim() function at all, “trimmed” is the name of the array i am iterating over

#4

that’s what you wrote in the function

or you mention all properties you want to keep

or, you could iterate over the array of objects and proceed in a different way:

  • save the property value in a variable
  • use the delete keyword to remove the property from the object
  • add new property with dot or beacket notation
#5

@Stivis hey,

I dont know if you can rename the key with map, you could try something like this

 trimmed.forEach((obj) => {
    obj.typ = obj.objType
    delete obj.objType
    obj.name = obj.caption
    delete obj.caption     
  })
    console.log(trimmed)
1 Like
#6

Correct.
Meanwhile i have read some things and from what i understand,object is mutated, trying to keep rest of the object by using …spread operator. Don’t understand it quite much

#7

yes this is how you would do it if you wanted to change the value but not the key.

 const translated = trimmed.map((obj) => {
      return { 
         ...obj,
        obj.objType: 'new type', 
        obj.caption: 'new caption'
}
    })
#8

map returns a new array, and if you write an object literal (graph parenthesis with key value pairs inside) then you are also creating a new array for each element of the array, nothing is mutated

#9

Thanks a lot! this worked like a charm

#10

nothing is mutated because map() returns new array ?
I think i understand much better now. Thank you

#11

map returns a new array, but also you write {...} and that’s a new object

1 Like
#12