Kusiyana pakati pa null ndi undefined mu JavaScript

Kutchulidwa

Kugwiritsa ntchito kwachilendo kwa null

Monga gawo lantchito, zikutanthauza kuti gawo la ntchito silinthu

            function myFn(obj) {
    if(null == obj) {
        // code
    }
}
        

Kumapeto kwa unyolo wazinthu

            Object.getPrototypeOf(Object.prototype);
        

Mukamasula zosinthazo, perekani zosasinthasintha

            let o={
 code:'abc'
};
o = null;
        

Kugwiritsa ntchito kosasinthika

Zosinthazi zalengezedwa koma sizinapatsidwe, phindu la zosinthazi silinafotokozeredwe

            let o;
console.log(o);    //undefined
        

Chizindikiro chomwe ntchitoyi ikuyenera kupereka sichinaperekedwe poyimba, ndiye kuti phindu la parameter lomwe silinaperekedwe silinafotokozeredwe

            function myFn(o) {
    console.log(o);
}
myFn();   //undefined
        

Malo omwe mulibe chinthucho, mtengowo ulibe tanthauzo

            let o={
 code:'abc'
};
console.log(o.name);    //undefined
        

Ntchitoyo ikapanda kubweza mtengo, imabwereranso mosasinthika mosasintha

            function myFn(obj) {
    obj = 'a';
}
console.log(myFn());    //undefined
        

Zofanana pakati pa null ndi undefined

Zonama mutatembenuzidwa kukhala boolean

            console.log(Boolean(null));  // false
console.log(Boolean(undefined)); // false
        

Kusiyana pakati pa null ndi undefined

Zotsatira zake ndizosiyana ndikasinthidwa kukhala nambala.Zotsatira zakusintha kosakwanira ndi nambala yolondola ya 0, ndipo zotsatira zakusintha kosadziwika ndi NaN.

            console.log(Number(null));  // 0
console.log(Number(undefined)); // NaN
        

Mitundu iwiriyi ndiyosiyana, mtundu wachabechabe ndichinthu, ndipo mtundu wa undefined ndiwosadziwika.

            console.log(typeof null); //object
console.log(typeof undefined); //undefined
        

yerekezerani zopanda pake ndi zosasinthika

Kusiyanitsa pakati pa zopanda pake ndi zosafotokozedwa, kuphatikiza kokha ndi komwe kungagwiritsidwe ntchito.

            console.log(Boolean(null == undefined));  // true
console.log(Boolean(null === undefined)); // false
        

Powombetsa mkota

Pambuyo poyerekeza pamwambapa, tikumvetsetsa bwino mitundu iwiriyi. Nthawi zambiri tikamaweruza ngati kusinthaku kuli ndi phindu polemba nambala, sitiyenera kusiyanitsa pakati pa ziwirizi, ingogwiritsa ntchito ngati mtundu wa Boolean. Koma pakafunika kuweruza ngati malowo alipo, tiyenera kugwiritsa ntchito mtunduwo kuweruza osadziwika. Pomaliza, ngati titadutsa mtengo manambala, tiyenera kupanga chigamulo choyamba, ndipo sitingaponyedwe mwachindunji ku mtundu wa manambala, apo ayi chopanda pake chingatipangitse kupeza zotsatira zosazolowereka, ndipo osadziwika adzawerengera zotsatira zosayenera za NaN.