How to Replace Values in a JSON Array (Without Breaking It)

Replacing values in a JSON array depends on whether you know the exact index of the item or if you need to search for it based on a property.

Doing it wrong can mutate your original data or break the structure entirely. Let's look at the right way to do it.

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1. Replacing by Index

If you know exactly which item in the array you want to change, you can target it directly by its index.

const users = [
  { id: 1, name: "Alice" },
  { id: 2, name: "Bob" }
];

// Replace the second item entirely
users[1] = { id: 2, name: "Robert" };

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2. Replacing a Property in an Object (using map)

If you want to keep the array structure but update a specific property across all items, use map(). This creates a new array, which is best practice if you want to avoid mutating the original data.

const updatedUsers = users.map(user => {
  if (user.id === 2) {
    return { ...user, name: "Robert" };
  }
  return user;
});

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3. Finding and Replacing in Deeply Nested Arrays

If your JSON has arrays inside objects inside arrays, a simple .map() won't be enough. You need a recursive function to traverse the entire structure and replace the value wherever it's found.

function replaceDeep(obj, target, replacement) {
  if (Array.isArray(obj)) {
    return obj.map(item => replaceDeep(item, target, replacement));
  } else if (obj !== null && typeof obj === 'object') {
    const newObj = {};
    for (const key in obj) {
      newObj[key] = replaceDeep(obj[key], target, replacement);
    }
    return newObj;
  }

  // If the current value matches the target, replace it
  return obj === target ? replacement : obj;
}

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Common Gotchas

• Reference vs Value: If you are replacing objects, make sure you are creating a new object ({ ...obj }) rather than just modifying the reference, or you might accidentally mutate the original JSON.
• Regex vs String: Simple .replace() only replaces the first match in a string. If you want to replace all occurrences, you need a global regex (/target/g).
• Null values: Remember that typeof null === 'object', so you must check for obj !== null before recursing.

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The Visual Way

Writing recursive scripts is fine for code, but if you just need to replace a specific value or pattern across a massive JSON payload once, writing a script is overkill.

If you want to find and batch replace targeted values, patterns, or data types across nested JSON visually, I built a free JSON Value Replacer.

Try it here

100% client-side. Nothing uploaded.

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Have you ever accidentally mutated a JSON object and spent hours debugging it? Let me know in the comments.