Transform values from a JSON representation

When transforming a given variable to the JSON representation, we might see unexpected results if the variable contains an unserializable property.

Let's consider a simple object that represents the information of a person. It has the `phones` property that is a set of different phone numbers.

const person = {
    name: 'John Doe',
    ages: 42,
    phones: new Set(['123', '456', '789']),
};

The set is transformed to an empty object which is unexpected output:

JSON.stringify(person);

// "{"name":"John Doe","ages":42,"phones":{}}"

We can solve the issue by passing the second parameter to the `stringify` function. It can be a function of two parameters representing the key and value of the current iterated item.

JSON.stringify(variable, (key, value) => {
    // The return value will be used in final output

    // If the function returns `undefined`,
    // the item will be excluded from the output
    return ...;
});

Here is how the phone numbers are transformed when we see the `phones` key:

JSON.stringify(person, (key, value) => (key === 'phones' ? [...value.values()] : value));

// "{"name":"John Doe","ages":42,"phones":["123","456","789"]}"

Want to transform all `Set` values? No problem!

JSON.stringify(person, (key, value) => (value instanceof Set ? [...value.values()] : value));

Transform values from a JSON representation

See also