[nerv_]

krutoy, на здоровье

/**
 * Inherits a target (Class_1) from a source (Class_2)
 * @param {Function} target
 * @param {Function} source
 */
function inherit(target, source) {
    target.prototype = Object.create(source.prototype);
    target.prototype.constructor = target;
    target.super_ = source;
}

// ---------------------

function FormField(data) {
    this._d = data;
}

// -------------------------

inherit(FormFile, FormField);

function FormFile(data, opts) {
    FormFile.super_.apply(this, arguments);
    this.opts = opts;
}

// -------------------------

var a = new FormFile(1, 2);
var b = new FormFile(10, 22);
console.log(a, a instanceof FormField, b instanceof FormField);
console.log(b, a instanceof FormFile, b instanceof FormFile);