Te rereketanga i waenga i te kore me te kore tautuhia i te JavaScript

Tohutoro

Tuhinga o mua

Hei waahanga mahi, ko te tikanga ko te waahanga mahi ehara i te mea

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

Hei mutunga o te mekameka tauira tauira

            Object.getPrototypeOf(Object.prototype);
        

Ka tukuna ana te taurangi, tohua te kore ki te taurangi

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

Tuhinga o mua kaore i tautuhia

Ko te taurangi e kiia ana engari kaore i tohaina, kaore i tautuhia te uara o te taurangi

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

Ko nga tohu e tika ana kia hoatuhia e te mahi kaore i te wa e waea ana, katahi ka tautuhia te uara o te waahanga kaore i te hoatuhia

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

Nga taonga kaore i roto te mea, kaore ano kia tautuhia te uara

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

Ki te kore te mahi e whakahoki i tetahi uara, ka hoki mai ano ka kore e tautuhia

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

Nga ritenga i waenga i te koretake me te kore kua tautuhia

Hape ka hurihia hei boolean

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

Te rereketanga i waenga i te koretake me te kore kua tautuhia

He rereke te hua ka hurihia ana ki te tau. Ko te hua o te hurihuri koretake he uara tau whaimana mo te 0, a ko te hua o te tahuritanga kaore i tautuhia ko NaN.

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

He rereke nga momo e rua, ko te momo null he ahanoa, a ko te momo kaore i tautuhia kaore i tautuhia.

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

whakataurite he kore me te kore tautuhia

Hei wehewehe i waenga i te koretake me te kore tautuhia, ko te whakakotahi anake ka taea te whakamahi. I te whakakotahi, ka whakataurite mena he orite nga momo e rua.

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

ki te whakarapopototanga

I muri i te whakataurite i runga ake nei, he maarama taatau ki enei momo momo e rua I te nuinga o te waa ka whakaarohia mena he uara whai mana te taurangi ka tuhi waehere ana, kaore e hiahiatia te wehewehe i waenga i nga mea e rua, me whakamahi noa hei momo Boolean. Engari me whakawa taatau mena kei te noho te kaainga, me tino whakamahi e taatau te momo hei whakawa whakawa kore. Hei whakamutunga, ki te paahitia e tatou tetahi uara tau, me whakatau e maatau te tuatahi, a kaore e taea te tuku tika ki tetahi momo taatai, ka kore ka kore he hua e puta mai i a tatou, ana ma te kore e tautuhia ka tatau tika te hua NaN