function shallowCopy(object) {
    if (object instanceof Date) {
        return new Date(+object);
    }
    var copy = {};
    for (var key in object) {
        if (object.hasOwnProperty(key)) {
            copy[key] = object[key];
        }
    }
    return copy;
}
 
var a = { x: 1, y: 2, z: [1, 2, 3] };
var b = shallowCopy(a); // b — это отдельный объект
b.x = 10;
console.log(a.x); // 1
 
// Но a.z и b.z указывают на один и тот же массив:
b.z.push(4);
console.log(a.z); // [1, 2, 3, 4]
 
var c = new Date(2014, 1, 1);
var d = shallowCopy(c);
d.setFullYear(2015);
console.log(c.getFullYear()); // 2014

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