JavaScript - Add an item to an object array depending on index

Question

I have an object array to which I'm add a new property ( theNewFieldToAdd ) using map , however I only want to add the property if the index is of a certain number.

Any ideas?

rows.map((row, index) => ({
   ...row,
   theNewFieldToAdd: true
})),

Answer 1

Would a ternary work?

 let x = [ {a: 1, b: 2}, {a: 3, b: 4}, {a: 5, b: 6}, {a: 7, b: 8} ]; console.log( x.map( (row, i) => (i > 2? {...row, newValue: true}: row) ) );

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Answer 2

rows.map((row, index) => ({
   ...row,
   ...(index===MYINDEX ? {theNewFieldToAdd: true} : {})
}))

Even more concise...

rows.map((row, index) => ({
  ...row,
  ...index===MYINDEX && {theNewFieldToAdd: true}
}))

Answer 3

you don't have to make it short. logics like this can pay off to be readable.

rows.map((row, index) => {
   if(index === x){
     row.theNewField = true
   }

   return row;
})

Answer 4

Try below working demo-

 rows = [{'first': 1},{'second': 2},{'third': 3},{'fourth': 4},{'fifth': 5}]; rows1 = rows.map((row, index) => (index == 1? {...row, theNewFieldToAdd: true }: row)); console.log(rows1);

Answer 5

You can use for example the short-circuit evaluation to make it a bit more concise:

 let rows = [{ key: "a" }, { key: "b" }, { key: "c" }]; let result = rows.map((row, index) => ({...row, ...(index === 0 && { theNewFieldToAdd: true }), })); console.log(result);