this inapatikana kulingana na jinsi kitendaji kinaitwa, si mahali ambapo kinafafanuliwa. Kuna kanuni tano:
js
obj = {
: ,
() { .; },
};
obj.();
f = obj.;
();
f.(obj);
();
this inapatikana kulingana na jinsi kitendaji kinaitwa, si mahali ambapo kinafafanuliwa. Kuna kanuni tano:
obj = {
: ,
() { .; },
};
obj.();
f = obj.;
();
f.(obj);
();
Kitendaji cha mshale haina this yake mwenyewe — kinairithi kutokana na scope inayoizunguka wakati wa ufafanuzi. Hii ndiyo sababu mishale ni bora kwa callbacks:
const obj = {
items: [1, 2],
logAll() {
// ✅ arrow inherits `this` from logAll → `this` is obj
this.items.forEach(i => console.log(this.items, i));
// ❌ a regular function here would have its own `this` (undefined) → crash
// this.items.forEach(function (i) { console.log(this.items); });
},
};
Kupitisha njia kama callback kupoteza urafiki wake, kwa sababu inaitwa tu kwa kawaida:
button.addEventListener("click", obj.getX); // ❌ `this` is the button
button.addEventListener("click", () => obj.getX()); // ✅ keeps obj
button.addEventListener("click", obj.getX.bind(obj)); // ✅ also fine
Kufahamu vibaya this ni moja ya matatizo ya kawaida ya JS.
Suluhisho ni kawaida kitendaji cha mshale au .bind() kukamatia this inayolengwa.