new.target是es6特性？？ 這兩處分別代表啥

請(qǐng)教
let PersonType2 = (function() {

"use strict";
const PersonType2 = function(name) {
    // 確認(rèn)函數(shù)被調(diào)用時(shí)使用了 new
    if (typeof new.target === "undefined") {
        // 這兩處new.target分別代表啥
        throw new Error("Constructor must be called with new.");
    }
    this.name = name;
}
Object.defineProperty(PersonType2.prototype, "sayName", {
    value: function() {
        // 確認(rèn)函數(shù)被調(diào)用時(shí)沒(méi)有使用 new
        if (typeof new.target !== "undefined") {
            // 這兩處new.target分別代表啥
            throw new Error("Method cannot be called with new.");
        }
        console.log(this.name);
    },
    enumerable: false,
    writable: true,
    configurable: true
});
return PersonType2;

}());