I have this for example:

const sample = [
  { id: 1, val1: 0, val4: 10 },
  { id: 10, val1: 1, val4: 10, val19: 0, val29: 0 },
  { id: 11, val1: 0, val4: 0, val19: 0, val29: 10 },
];

and I want to change every 0 value into null

const sample = [
  { id: 1, val1: null, val4: 10 },
  { id: 10, val1: 1, val4: 10, val19: null, val29: null },
  { id: 11, val1: null, any: null, sample: null, val29: 10 },
];

I know I need to use map but I'm having difficulty in accessing every object.

I have this for example:

const sample = [
  { id: 1, val1: 0, val4: 10 },
  { id: 10, val1: 1, val4: 10, val19: 0, val29: 0 },
  { id: 11, val1: 0, val4: 0, val19: 0, val29: 10 },
];

and I want to change every 0 value into null

const sample = [
  { id: 1, val1: null, val4: 10 },
  { id: 10, val1: 1, val4: 10, val19: null, val29: null },
  { id: 11, val1: null, any: null, sample: null, val29: 10 },
];

I know I need to use map but I'm having difficulty in accessing every object.

• javascript
• typescript
• ecmascript-6

• by value do you mean val1, val2, etc...? – Dalorzo Commented Sep 16, 2020 at 5:59
• Please visit the help center, take the tour to see what and How to Ask. Do some research, search for related topics on SO; if you get stuck, post a minimal reproducible example of your attempt, noting input and expected output using the [<>] snippet editor. – mplungjan Commented Sep 16, 2020 at 6:00

8 Answers 8

If you have no methods this might work too.

You stringify it and use an replacer function to replace all zeros to null. Then just parse it back.

Works for deeper nested objects aswell

const sample = [
  { id: 1, val1: 0, val4: 10 },
  { id: 10, val1: 1, val4: 10, val19: 0, val29: 0 },
  { id: 11, val1: 0, val4: 0, val19: 0, val29: 10 },
];

let str = JSON.stringify(sample,(k, v) =>  v === 0 ? null : v);
let result = JSON.parse(str);

console.log(result);

You may want to do loop through the list and then for every property in the object you check for val

const sample = [
  { id: 1, val1: 0, val4: 10 },
  { id: 10, val1: 1, val4: 10, val19: 0, val29: 0 },
  { id: 11, val1: 0, val4: 0, val19: 0, val29: 10 },
];

let sample1 = sample[0]; //<<-- you may loop through your entire array

for (const [key, value] of Object.entries(sample1)) {
  if (key.lastIndexOf('val')>=0 && value === 0){
       sample1[key] = null;
   }
}

console.log(sample1)

You need forEach if you do not want a new array

const sample = [ { id: 1, val1: 0, val4: 10 }, { id: 10, val1: 1, val4: 10, val19: 0, val29: 0 }, { id: 11, val1: 0, val4: 0, val19: 0, val29: 10 }];

sample.forEach(item => { 
  for (val in item) item[val] = item[val] === 0 ? null : item[val] 
});
console.log(sample)

You can use this, but you need let to reuse the variable name

let sample = [
  { id: 1, val1: 0, val4: 10 },
  { id: 10, val1: 1, val4: 10, val19: 0, val29: 0 },
  { id: 11, val1: 0, val4: 0, val19: 0, val29: 10 },
];
sample = sample.map(obj => {
  Object.keys(obj).forEach(key => {
    obj[key] = obj[key] || null;
  });
  return obj;
});

console.log(sample)

This is basically getting the keys of each object then checking value of object against that key in obj[key] = obj[key] || null. So when obj[key] will be either 0, null or undefined, it will bee equal to null, otherwise it won't update.

This is what Array.prototype.map was made for, it takes a function as a parameter, that is called once for each element of the array, while providing the element itself as an argument. The.map function returns a new set and does not directly modify the original. Whatever the return value is for the parameter function for each element is, bees the new value of that element in the newly constructed array.

In your case though it is a bit more plicated since each element itself is an object, so we can convert each object to an array, map is own properties, and return the reconstructed object to our main .maps parameter function

So..

sample=sample.map(function (currentElement){
    return (typeof(currentElement) == "object" ?
        Object.fromEntries(
            Object.entries(
                currentElement
            ).map(function (prop){
                return prop === 0 ? null : prop
            })
        ) : currentElement
    )
})

I have an solution using map only, may help:

var sample = [
    { id: 1, val1: 0, val4: 10 },
    { id: 10, val1: 1, val4: 10, val19: 0, val29: 0 },
    { id: 11, val1: 0, val4: 0, val19: 0, val29: 10 },
  ]; 
var output = sample.map((item) => {
      Object.keys(item).map((key) => {
        item[key] = (item[key] == 0 ? null : item[key]); return item[key]
      });
      return item;
  });
  
  console.log(output);

You can use "for...in" to access every object

Demo Here

const sample = [
  { id: 1, val1: 0, val4: 10 },
  { id: 10, val1: 1, val4: 10, val19: 0, val29: 0 },
  { id: 11, val1: 0, val4: 0, val19: 0, val29: 10 },
];

sample.map((s) => {
  for (let i in s) if (s[i] === 0) s[i] = null;
  return s;
});
console.log(sample);

Immutable Style

const sample: Record<string, unknown>[] = [
  { id: 1, val1: 0, val4: 10 },
  { id: 10, val1: 1, val4: 10, val19: 0, val29: 0 },
  { id: 11, val1: 0, val4: 0, val19: 0, val29: 10 }
]

const updated = sample.map((rec) =>
  Object.keys(rec).reduce<Record<string, unknown>>(
    (acc, key) => (rec[key] == 0 ? { ...acc, [key]: null } : { ...acc, [key]: rec[key] }),
    {}
  )
)

console.log(updated)
// OUTPUT
// [
//   { id: 1, val1: null, val4: 10 },
//   { id: 10, val1: 1, val4: 10, val19: null, val29: null },
//   { id: 11, val1: null, val4: null, val19: null, val29: 10 }
// ]