Use all() to turn an array of promises into a promise to an array.
Promise.all([
56 | value1,
57 | value2,
58 | value3,
59 | ])
60 | ->
62 | [value1
63 | value2,
64 | value3]If any promise is rejected, the error will be passed through.
70 |Promise.all([
72 | ,
73 | ,
74 | error,
75 | ])
76 | ->
78 | error
79 | Use race() instead to pass through the first settled promise.
Promise.race([
86 | ,
87 | ,
88 | value,
89 | ])
90 | ->
92 | value
93 | Calls onFulfilled once the promise is fulfilled.
118 | value.then(value => nextValue, ...) -> nextValue
119 |
120 |
121 | value.then(value => outcome, ...) -> outcome
122 |
123 |
124 | value.then(value => throw error, ...) -> error
125 |
126 |
127 | Calls onRejected if the promise is rejected.
130 | error.then(..., error => value) -> value
131 |
132 |
133 | error.then(..., error => outcome) -> outcome
134 |
135 |
136 | error.then(..., error => throw nextError) -> nextError
137 |
138 |
139 | Passes errors through if onRejected is undefined.
142 | error.then(...) -> error
143 |
144 |
145 | Behaves identically to then when onFulfilled is omitted.
155 | error.catch(onRejected) <=> error.then(..., onRejected)
156 |
157 |
158 | Passes fulfilled values through.
159 | 160 |
161 | value.catch(...) -> value
162 |
163 | Calls onFinally with no arguments once any outcome is available. Passes through input promise.
171 | outcome.finally(() => ...) -> outcome
172 |
173 |
174 |
175 | The onFulfilled, onRejected and onFinally functions will not be executed until at least the next tick, even for promises that already have an outcome.
176 |
The function passed to new Promise will be executed synchronously.
new Promise((resolve, reject) => {
191 | doImportantStuff((error, value) => {
192 | if (error)
193 | reject(error)
194 | else
195 | resolve(value)
196 | })
197 | })Use resolve() or reject() to create promises from values.
Promise.resolve(value) -> value
203 | Promise.reject(error) -> error
204 | If you put a fulfilled promise into a fulfilled promise, they'll collapse into one.
205 |Promise.resolve(value) -> value
206 | Sometimes you might not need reject, or might not resolve to a value.
function delay(milliseconds) {
210 | return new Promise(resolve =>
211 | setTimeout(resolve, milliseconds)
212 | )
213 | }Calling an async function always results in a promise.
229 | (async () => value)() -> value
230 |
231 |
232 | (async () => outcome)() -> outcome
233 |
234 |
235 | (async () => throw error)() -> error
236 |
237 |
238 | await waits for a promise to be fulfilled, then returns its value.
async function() {
241 | try {
242 | let value = await outcome
243 | // ...
244 | }
245 | catch (error) {
246 | // ...
247 | }
248 | }
249 | You can pass non-promise values to await
const fn = async () => {
254 | let value = await value
255 | // ...
256 | }
257 |
260 | await may only be used within async functions.
261 |
264 | await will wait until at least the next tick before returning, even when awaiting already-fulfilled promises or non-promise values.
265 |