Question 172706 in Javascript Question posted in
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Can Javascript replace a nested object’s value if the key exists?

I have an array with nested objects. What I want to achieve is to loop through the arrays objects and check if a key exists inside the object and if it does I want to replace the value of that object and break out of the loop. If the key doesn’t exist inside any of the objects I want to append a new object into the array and print the final array. What I tried below is not working. Where did I go wrong and how can I fix it? Thanks in advance.

x = [{
  "s": "23",
  "t": "41"
}, {
  "e": "29",
  "t": "87"
}]

for (var i = 0; i < x.length; i++) {
  if ("d" in x[i]) {
    x[i]["t"] = "21"
    console.log(x)
    break
  } else if (i === x.length - 1) {
    x.push({
      "v": "22",
      "t": "77"
    })
    console.log(x)

    //loop finised
  }
}
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2

Answers


  1. 0

    The reason your code isn’t working because it enters an infinite loop. You’re mutating the array directly(by adding/pushing a new element) while looping through it. So the length keeps getting longer & longer resulting in infinite loop.

    Just change your code to the following:

    x = [{
  "s": "23",
  "t": "41"
}, {
  "e": "29",
  "t": "87"
}]

let isKeyExists = false;

for (var i = 0; i < x.length; i++) {
  if ("d" in x[i]) {
    x[i]["t"] = "21"
    console.log(x)
    isKeyExists = true;
    break
  }  
}

if (!isKeyExists) {
  x.push({
      "v": "22",
      "t": "77"
  })
}

console.log(x)

    In the code above, you just add the object after you have exited the loop.

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  2. 0

    Your code is not working because you are trying to access the d key in the x array, but the d key does not exist in any of the objects in the x array. You can fix this by checking if the d key exists in the current object before you try to access it. You can do this by using the hasOwnProperty() method.

    Here is the corrected code:

    x = [{
  "s": "23",
  "t": "41"
}, {
  "e": "29",
  "t": "87"
}]

for (var i = 0; i < x.length; i++) {
  if (x[i].hasOwnProperty("d")) {
    x[i]["t"] = "21"
    console.log(x)
    break
  } else if (i === x.length - 1) {
    x.push({
      "v": "22",
      "t": "77"
    })
    console.log(x)

    //loop finised
  }
}
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