What's the most efficient way to turn all the keys of an object to lower case - JavaScript?

When working with JavaScript objects, you may need to convert all property keys to lowercase for consistency. Here's how to efficiently transform object keys using built-in JavaScript methods.

Sample Object

Let's start with an object that has uppercase keys:

var details = {
    "STUDENTNAME": "John",
    "STUDENTAGE": 21,
    "STUDENTCOUNTRYNAME": "US"
};
console.log("Original object:", details);

Original object: { STUDENTNAME: 'John', STUDENTAGE: 21, STUDENTCOUNTRYNAME: 'US' }

Method 1: Using Object.keys() and while Loop

This approach uses a while loop to iterate through object keys and create a new object with lowercase keys:

var details = {
    "STUDENTNAME": "John",
    "STUDENTAGE": 21,
    "STUDENTCOUNTRYNAME": "US"
};

var tempKey, allKeysOfDetails = Object.keys(details);
var numberOfKey = allKeysOfDetails.length;
var allKeysToLowerCase = {};

while (numberOfKey--) {
    tempKey = allKeysOfDetails[numberOfKey];
    allKeysToLowerCase[tempKey.toLowerCase()] = details[tempKey];
}

console.log("Lowercase keys:", allKeysToLowerCase);

Lowercase keys: { studentcountryname: 'US', studentage: 21, studentname: 'John' }

Method 2: Using Object.entries() and reduce() (More Efficient)

A more modern and concise approach using ES6 methods:

var details = {
    "STUDENTNAME": "John",
    "STUDENTAGE": 21,
    "STUDENTCOUNTRYNAME": "US"
};

var lowercaseObject = Object.entries(details).reduce((acc, [key, value]) => {
    acc[key.toLowerCase()] = value;
    return acc;
}, {});

console.log("Using reduce:", lowercaseObject);

Using reduce: { studentname: 'John', studentage: 21, studentcountryname: 'US' }

Method 3: Using Object.fromEntries() (ES2019)

The most concise approach using the latest JavaScript features:

var details = {
    "STUDENTNAME": "John",
    "STUDENTAGE": 21,
    "STUDENTCOUNTRYNAME": "US"
};

var lowercaseObject = Object.fromEntries(
    Object.entries(details).map(([key, value]) => [key.toLowerCase(), value])
);

console.log("Using fromEntries:", lowercaseObject);

Using fromEntries: { studentname: 'John', studentage: 21, studentcountryname: 'US' }

Performance Comparison

Conclusion

For maximum compatibility, use the while loop approach. For modern applications, Object.fromEntries() with map() provides the cleanest and most readable solution.