__proto__ is an old, deprecated feature of JavaScript. The proper way to get the prototype of an object is with Object.getPrototypeOf(object) and use Object.setPrototypeOf(object) to set a prototype.

I'm assuming in this example what the web app is doing is it is using the name of the child as the key in a object like this:

    students[studentName] = studentDetails;

Since the child's name is __proto__ the web app is setting:

    students['__proto__'] = studentDetails;

Which is the same as:

    students.__proto__ = studentDetails;

Which sets the prototype of the object full of students to the student's details, and will totally break things.

There is no reason to use a library like stringset.js or stringmap.js with extra overhead. The proper solution is to never use user supplied strings as keys in an object. A good key to use in this situation for an object full of students would be a generated student ID or something like that.