TypeScript JSON decorator to turn convert ES6 class properties from camelCaseLikeThis to snake_case_like_this to be used as an HTTP request JSON object.

json-decorator.ts

function JSON<T extends {new(...args: any[]): {}}>(ctor: T) {
    function toSnakeCase(prop: string): string {
        return prop.replace(/[A-Z]/g, (prop: string): string => {
            return `_${prop.toLowerCase()}`;
        });
    }

    return class extends ctor {
        constructor(...args: any[]) {
            let cfg = args.shift();

            for (let prop in cfg) {
                if (Object.prototype.hasOwnProperty.call(cfg, prop)) {
                    cfg[toSnakeCase(prop)] = cfg[prop];
                    delete cfg[prop];
                }
            }

            super(cfg, ...args);
        }
    }
}

@JSON
class Person {
    id: number;
    firstName: string;
    lastName: string;
    homePhoneNumber: string;
    cellPhoneNumber: string;

    constructor(values: Object = {}) {
        Object.assign(this, values);
    }
}

let snake_case_json_object = new Person({
    id: 0,
    firstName: 'John',
    lastName: 'Doe',
    homePhoneNumber: '1-800-555-1337',
    cellPhoneNumber: '1-800-555-1337'
});

console.log(snake_case_json_object);
// {
//     "first_name": "John",
//     "last_name": "Doe",
//     "home_phone_number": "1-800-555-1337",
//     "cell_phone_number": "1-800-555-1337",
// }