Uppercase or lowercase object keys in JavaScript

Data processing often requires transformation of structures to conform to a specific format. A very simple example of this is converting all the keys of an object to upper or lower case, an easy task for JavaScript.

Uppercase object keys

In order to convert all the keys of an object to upper case, we first need to obtain an array of the object's keys, using Object.keys(). Then, use Array.prototype.reduce() to map the array to an object, using String.prototype.toUpperCase() to uppercase the object's keys.

const upperize = obj =>
  Object.keys(obj).reduce((acc, k) => {
    acc[k.toUpperCase()] = obj[k];
    return acc;
  }, {});

upperize({ Name: 'John', Age: 22 }); // { NAME: 'John', AGE: 22 }

Lowercase object keys

Similarly, to convert all the keys of an object to lower case, we can use the same approach. The only notable difference is that we use String.prototype.toLowerCase() to lowercase the object's keys.

const lowerize = obj =>
  Object.keys(obj).reduce((acc, k) => {
    acc[k.toLowerCase()] = obj[k];
    return acc;
  }, {});

lowerize({ Name: 'John', Age: 22 }); // { name: 'John', age: 22 }