Check if the value of a variable exists in an object

Question

I have a Typescript project where I need to know if the value of a variable is in any property of the Object.

This is the object:

let listDump = [
   {
     "properties":{
        "title":"CARS"
     }
  },
  {
     "properties":{
        "title":"HOME"
     }
  },
  {
     "properties":{
        "title":"COUNTRY"
     }
  }
];

This is the declared variable:

let newData = 'ANIMALS'

This is what I do to check if it exists:

for (let sheet of listDump) {
  if (sheet.properties.title == newData) {
    console.log(`do not create property`)
  } else {
    console.log('create property') 
  }
}

Problem: Doing three checks operates three times on the else

What I need to know is how to check that it exists without needing to iterate over the object and operate only once in case it doesn't exist

Does this answer your question? [Check if a key exists inside a JSON object](https://stackoverflow.com/questions/20804163/check-if-a-key-exists-inside-a-json-object) — Søren Eriksen, Jan 25 '22 at 14:44
@stark, you can't get away from iterating over the array. At least `some` will stop at the first match. — Andy, Jan 25 '22 at 14:49
@Andy i think they just wanted a clean way to avoid logging 3 times — skara9, Jan 25 '22 at 14:51
Does this answer your question? [Find object by id in an array of JavaScript objects](https://stackoverflow.com/questions/7364150/find-object-by-id-in-an-array-of-javascript-objects) — evolutionxbox, Jan 25 '22 at 15:00

score 3 · Accepted Answer · answered Jan 25 '22 at 14:45

3

You can use <Array>.some

listDump.some(sheet => sheet.properties.title == newData) // returns true | false

answered Jan 25 '22 at 14:45

skara9

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I have changed the value of the variable, now it is in the JSON object. When I do `listDump.some(sheet => sheet.properties.title == fileName)` out `true`, but when I do `listDump.some(sheet => sheet.properties.title != fileName)` it comes out `true` too, why does this happen? How can I change the condition so that they are different? – stark Jan 25 '22 at 15:52
first one checks if any element has a title equal to filename, second checks if any element has a title other than filename ---- if you want to check if every element has a title other than filename replace `some` with `every` on the 2nd statement or add a not `!` to the beginning of the 1st statement – skara9 Jan 25 '22 at 16:02

Check if the value of a variable exists in an object

1 Answers1