Ni tofauti gani kati ya watch na watchEffect?

Question

Accepted Answer

Zote mbili zinaendesha athari za upande kama jibu la mabadiliko ya reaktizi, lakini hutofautiana kwa jinsi tegemezi ilivyoainishwa na taarifa gani wanakupa. Zitumie kwa athari za upande (API simu, kurekodi, kazi ya DOM inayoadhimiana) — **sio** kwa kuomba maadili (hiyo ni `computed`). ## watch — chanzo halisi, inatoa maadili ya zamani + mipya ```vue ``` `watch` inakingilia **mahususi** chanzo unachosema, inaendeza callback tu wakati chanzo hichi kinabadilika, na inatoa maadili **ya zamani na mipya** — muhimu wakati unahitaji kulinganisha au kukabiliana na sehemu moja ya hali. ## watchEffect — kufuatilia tegemezi moja kwa moja, inaendeza haraka ```vue ``` `watchEffect` **kufuatilia moja kwa moja** kila thamani ya reaktizi inayotumiwa ndani yake (hakuna orodha ya chanzo), na inaendeza **haraka katika aina** (kisha inaendezeleza upya kwa badiliko lolote la tegemezi). Hakuna maadili ya zamani/mipya. ## Upande kwa upande ```text watch watchEffect Dependencies explicit (you name them) automatic (tracked from usage) Runs immediately? no (unless immediate:true) yes Old + new values? yes no Best for reacting to specific state, running an effect that depends needing prev value on several values ``` ## Chaguo muhimu la watch ```js watch(source, cb, { immediate: true, // run once right away (like watchEffect) deep: true, // watch nested object changes }); watch([a, b], ([newA, newB]) => {}); // watch multiple sources ``` ## Kwa nini kumuhimu Kuchagua zana sahihi huweka athari za upande za reaktizi safi: tumia **`computed`** kwa maadili yaliyotengana, **`watch`** wakati unahitaji kukabiliana na chanzo mahususi au kulinganisha zamani/mpya (mfano nkumbuka wakati kitambulisho kinabadilika), na **`watchEffect`** kwa athari zinazotegemeza thamani kadhaa na inapaswa kuzifuatilia moja kwa moja. Kutumia vibaya waangazi kwa mgombea (badala ya `computed`) ni muundo wa kawaida wa kupinga.