Promise.all:
promise數(shù)組中所有狀態(tài)變?yōu)閒ulfilled,Promise.all才會(huì)變成fulfilled
promise數(shù)組中有一個(gè)變?yōu)閞ejected,Promise.all就會(huì)變成rejected
Promise.race:
promise數(shù)組中有一個(gè)狀態(tài)變?yōu)閒ulfilled,Promise.race就變成fulfilled
promise數(shù)組中有一個(gè)變?yōu)閞ejected,Promise.race就會(huì)變成rejected
Promise.allSettled:
狀態(tài)只有fulfilled,then返回值為
[{"status":"fulfilled","value":100},{"status":"rejected","reason":50},{"status":"fulfilled","value":200}]
Promise.any:
promise數(shù)組中有一個(gè)狀態(tài)變?yōu)閒ulfilled,Promise.any就變成fulfilled
promise數(shù)組中有全部變?yōu)閞ejected,Promise.any才會(huì)變成rejected
Promise.resolve:
1.參數(shù)是一個(gè) Promise 實(shí)例
如果參數(shù)是 Promise 實(shí)例,那么Promise.resolve將不做任何修改、原封不動(dòng)地返回這個(gè)實(shí)例。
2.參數(shù)是一個(gè)thenable對(duì)象
Promise.resolve()方法會(huì)將這個(gè)對(duì)象轉(zhuǎn)為 Promise 對(duì)象,然后就立即執(zhí)行thenable對(duì)象的then()方法,thenable對(duì)象的then()方法執(zhí)行后,對(duì)象p的狀態(tài)就變?yōu)閞esolved,從而立即執(zhí)行最后那個(gè)then()方法指定的回調(diào)函數(shù)
3.參數(shù)不是具有then()方法的對(duì)象,或根本就不是對(duì)象
如果參數(shù)是一個(gè)原始值,或者是一個(gè)不具有then()方法的對(duì)象,則Promise.resolve()方法返回一個(gè)新的 Promise 對(duì)象,狀態(tài)為resolved。由于字符串Hello不屬于異步操作(判斷方法是字符串對(duì)象不具有 then 方法),返回 Promise 實(shí)例的狀態(tài)從一生成就是resolved,所以回調(diào)函數(shù)會(huì)立即執(zhí)行。Promise.resolve()方法的參數(shù),會(huì)同時(shí)傳給回調(diào)函數(shù)
4.不帶有任何參數(shù)
Promise.resolve()方法允許調(diào)用時(shí)不帶參數(shù),直接返回一個(gè)resolved狀態(tài)的 Promise 對(duì)象。
知識(shí)點(diǎn):
Promise的面試題還是有很多的,不止有代碼輸出題,還有手寫(xiě)代碼,Promise原理,實(shí)現(xiàn)Promise A+等等