Update each element within array within single function

Question

I have below array object -

[
{
 index:0,
 value:"Yes",
},
{
 index:1,
 value:"No",
},
{
 index:2,
 value:"No",
},
{
 index:3,
 value:"Yes",
},
]

I want to update value of each element in array with "NA"

I tried doing -

obj.map(x=>{
x.value="NA"
});

This is not working.

You're not returning anything from the map callback. Try return x; after you've set the value. Note: map returns a new array. You may want forEach which can mutate the array instead - depends on your use-case. — Andy
– Andy, Commented Oct 13, 2022 at 11:12

hgb123 · Accepted Answer · 2022-10-13 11:23:31Z

1

You could use two ways

forEach, which would mutate the existing array

const obj = [
  {
    index: 0,
    value: "Yes",
  },
  {
    index: 1,
    value: "No",
  },
  {
    index: 2,
    value: "No",
  },
  {
    index: 3,
    value: "Yes",
  },
]

obj.forEach(x => {
  x.value = "NA"
})

console.log(obj)

map, which will return the new array

const obj = [
  {
    index: 0,
    value: "Yes",
  },
  {
    index: 1,
    value: "No",
  },
  {
    index: 2,
    value: "No",
  },
  {
    index: 3,
    value: "Yes",
  },
]

const newObj = obj.map(x => ({
  ...x,
  value: "NA",
}))

console.log(newObj)

answered Oct 13, 2022 at 11:23

hgb123

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3 Comments

C Sharper Over a year ago

can I assign it within same array ? (with map) .. Like - obj=obj.map(..

Andy Over a year ago

That's not how you should be using map. map transforms an array into a new array. @CSharper

hgb123 Over a year ago

@CSharper yes, you could, but you should not. Usually, map is used to create a new array based on the provided callback function (avoid mutation), while forEach is used only to execute the function on each element (mutation is okay)

flyingfox · Accepted Answer · 2022-10-13 11:19:05Z

1

There are two points need to pay attention:

you need to assign the result to a new variable after using map
inside the map function,we also need to return the mapped object via return

let data = [
{
 index:0,
 value:"Yes",
},
{
 index:1,
 value:"No",
},
{
 index:2,
 value:"No",
},
{
 index:3,
 value:"Yes",
},
]

let result = data.map(d =>{
  d.value="NA"
  return d
})

console.log(result)

answered Oct 13, 2022 at 11:19

flyingfox

13.5k4 gold badges30 silver badges43 bronze badges

Comments

Chanka1021 · Accepted Answer · 2022-10-13 11:23:18Z

0

let data = [
{
 index:0,
 value:"Yes",
},
{
 index:1,
 value:"No",
},
{
 index:2,
 value:"No",
},
{
 index:3,
 value:"Yes",
},
]

let arr= data.map(x =>{
  x.value="NA"
  return x
})

console.log(arr)

or with the old way

for(let i=0;i<data.lenght;i++){
data[i].value='na'
}
console.log(arr)

answered Oct 13, 2022 at 11:23

Chanka1021

718 bronze badges

3 Comments

flyingfox Over a year ago

Small advice,before post answer,need to check others have posted the same or not

Chanka1021 Over a year ago

@lucumt Small advice,before post answer,need to check others have posted the same or not

flyingfox Over a year ago

Hey,why do you copy my comments, your answer is 4 minutes later posted than me and is the same with mine,so try to avoid the duplicate answer

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