Cevabı oku.
Dayanağını gör.

Locating elements​ Playwright comes with multiple built-in locators. To make tests resilient, we recommend prioritizing user-facing attributes and explicit contracts such as page.getByRole(). For example, consider the following DOM structure.

If you have a list of identical elements, and the only way to distinguish between them is the order, you can choose a specific element from a list with locator.first(), locator.last() or locator.nth(). const banana = await page.getByRole('listitem').nth(1); However, use this method with caution. Often times, the page might change, and the locator will point to a completely different element from the one you expected. Instead, try to come up with a unique locator that will pass the strictness criteria.

You can explicitly opt-out from strictness check by telling Playwright which element to use when multiple elements match, through locator.first(), locator.last(), and locator.nth(). These methods are not recommended because when your page changes, Playwright may click on an element you did not intend. Instead, follow best practices above to create a locator that uniquely identifies the target element. More Locators​

Strictness​ Locators are strict. This means that all operations on locators that imply some target DOM element will throw an exception if more than one element matches. For example, the following call throws if there are several buttons in the DOM: Throws an error if more than one​ await page.getByRole('button').click(); On the other hand, Playwright understands when you perform a multiple-element operation, so the following call works perfectly fine when the locator resolves to multiple elements. Works fine with multiple elements​ await page.getByRole('button').count(); You can explicitly opt-out from strictness check by telling Playwright which element to use when multiple elements match, through locator.first(), locator.last(), and locator.nth(). These methods are not recommended because when your page changes, Playwright may click on an element you did not intend. Instead, follow best practices above to create a locator that uniquely identifies the target element.

Added in: v0.9.4 If a call to stream.write(chunk) returns false, the 'drain' event will be emitted when it is appropriate to resume writing data to the stream. // Write the data to the supplied writable stream one million times. // Be attentive to back-pressure.

Returns: <this> Destroy the stream. Optionally emit an 'error' event, and emit a 'close' event (unless emitClose is set to false). After this call, the writable stream has ended and subsequent calls to write() or end() will result in an ERR_STREAM_DESTROYED error. This is a destructive and immediate way to destroy a stream. Previous calls to write() may not have drained, and may trigger an ERR_STREAM_DESTROYED error. Use end() instead of destroy if data should flush before close, or wait for the 'drain' event before destroying the stream. const { Writable } = require('node:stream');

Added in: v0.9.4 History chunk <string> | <Buffer> | <TypedArray> | <DataView> | <any> Optional data to write. For streams not operating in object mode, chunk must be a <string>, <Buffer>, <TypedArray> or <DataView>. For object mode streams, chunk may be any JavaScript value other than null. encoding <string> | <null> The encoding, if chunk is a string. Default: 'utf8' callback <Function> Callback for when this chunk of data is flushed. Returns: <boolean> false if the stream wishes for the calling code to wait for the 'drain' event to be emitted before continuing to write additional data; otherwise true.

Tasks can easily and safely be cancelled. When a task is cancelled, asyncio.CancelledError will be raised in the task at the next opportunity. It is recommended that coroutines use try/finally blocks to robustly perform clean-up logic. In case asyncio.CancelledError is explicitly caught, it should generally be propagated when clean-up is complete. asyncio.CancelledError directly subclasses BaseException so most code will not need to be aware of it. The asyncio components that enable structured concurrency, like asyncio.TaskGroup and asyncio.timeout(), are implemented using cancellation internally and might misbehave if a coroutine swallows asyncio.CancelledError. Similarly, user code should not generally call uncancel. However, in cases when suppressing asyncio.CancelledError is truly desired, it is necessary to also call uncancel() to completely remove the cancellation state.

The async with statement will wait for all tasks in the group to finish. While waiting, new tasks may still be added to the group (for example, by passing tg into one of the coroutines and calling tg.create_task() in that coroutine). Once the last task has finished and the async with block is exited, no new tasks may be added to the group. The first time any of the tasks belonging to the group fails with an exception other than asyncio.CancelledError, the remaining tasks in the group are cancelled. No further tasks can then be added to the group. At this point, if the body of the async with statement is still active (i.e., __aexit__() hasn’t been called yet), the task directly containing the async with statement is also cancelled. The resulting asyncio.CancelledError will interrupt an await, but it will not bubble out of the containing async with statement. Once all tasks have finished, if any tasks have failed with an exception other than asyncio.CancelledError, those exceptions are combined in an ExceptionGroup or BaseExceptionGroup (as appropriate; see their documentation) which is then raised.

Two base exceptions are treated specially: If any task fails with KeyboardInterrupt or SystemExit, the task group still cancels the remaining tasks and waits for them, but then the initial KeyboardInterrupt or SystemExit is re-raised instead of ExceptionGroup or BaseExceptionGroup. If the body of the async with statement exits with an exception (so __aexit__() is called with an exception set), this is treated the same as if one of the tasks failed: the remaining tasks are cancelled and then waited for, and non-cancellation exceptions are grouped into an exception group and raised. The exception passed into __aexit__(), unless it is asyncio.CancelledError, is also included in the exception group. The same special case is made for KeyboardInterrupt and SystemExit as in the previous paragraph. Task groups are careful not to mix up the internal cancellation used to “wake up” their __aexit__() with cancellation requests for the task in which they are running made by other parties. In particular, when one task group is syntactically nested in another, and both experience an exception in one of their child tasks simultaneously, the inner task group will process its exceptions, and then the outer task group will receive another cancellation and process its own exceptions.

Assuming the library is compiled with foreign key constraints enabled, it must still be enabled by the application at runtime, using the PRAGMA foreign_keys command. For example: sqlite> PRAGMA foreign_keys = ON; Foreign key constraints are disabled by default (for backwards compatibility), so must be enabled separately for each database connection. (Note, however, that future releases of SQLite might change so that foreign key constraints enabled by default. Careful developers will not make any assumptions about whether or not foreign keys are enabled by default but will instead enable or disable them as necessary.) The application can also use a PRAGMA foreign_keys statement to determine if foreign keys are currently enabled. The following command-line session demonstrates this:

sqlite> PRAGMA foreign_keys; 0 sqlite> PRAGMA foreign_keys = ON; sqlite> PRAGMA foreign_keys; 1 sqlite> PRAGMA foreign_keys = OFF;

Tip: If the command "PRAGMA foreign_keys" returns no data instead of a single row containing "0" or "1", then the version of SQLite you are using does not support foreign keys (either because it is older than 3.6.19 or because it was compiled with SQLITE_OMIT_FOREIGN_KEY or SQLITE_OMIT_TRIGGER defined). It is not possible to enable or disable foreign key constraints in the middle of a multi-statement transaction (when SQLite is not in autocommit mode). Attempting to do so does not return an error; it simply has no effect.

Some PostgreSQL data types and functions have special rules regarding transactional behavior. In particular, changes made to a sequence (and therefore the counter of a column declared using serial) are immediately visible to all other transactions and are not rolled back if the transaction that made the changes aborts. See Section 9.17 and Section 8.1.4. 13.2.1. Read Committed Isolation Level Read Committed is the default isolation level in PostgreSQL. When a transaction uses this isolation level, a SELECT query (without a FOR UPDATE/SHARE clause) sees only data committed before the query began; it never sees either uncommitted data or changes committed by concurrent transactions during the query's execution. In effect, a SELECT query sees a snapshot of the database as of the instant the query begins to run. However, SELECT does see the effects of previous updates executed within its own transaction, even though they are not yet committed. Also note that two successive SELECT commands can see different data, even though they are within a single transaction, if other transactions commit changes after the first SELECT starts and before the second SELECT starts.

UPDATE, DELETE, SELECT FOR UPDATE, and SELECT FOR SHARE commands behave the same as SELECT in terms of searching for target rows: they will only find target rows that were committed as of the command start time. However, such a target row might have already been updated (or deleted or locked) by another concurrent transaction by the time it is found. In this case, the would-be updater will wait for the first updating transaction to commit or roll back (if it is still in progress). If the first updater rolls back, then its effects are negated and the second updater can proceed with updating the originally found row. If the first updater commits, the second updater will ignore the row if the first updater deleted it, otherwise it will attempt to apply its operation to the updated version of the row. The search condition of the command (the WHERE clause) is re-evaluated to see if the updated version of the row still matches the search condition. If so, the second updater proceeds with its operation using the updated version of the row. In the case of SELECT FOR UPDATE and SELECT FOR SHARE, this means it is the updated version of the row that is locked and returned to the client. INSERT with an ON CONFLICT DO UPDATE clause behaves similarly. In Read Committed mode, each row proposed for insertion will either insert or update. Unless there are unrelated errors, one of those two outcomes is guaranteed. If a conflict originates in another transaction whose effects are not yet visible to the INSERT, the UPDATE clause will affect that row, even though possibly no version of that row is conventionally visible to the command. INSERT with an ON CONFLICT DO NOTHING clause may have insertion not proceed for a row due to the outcome of another transaction whose effects are not visible to the INSERT snapshot. Again, this is only the case in Read Committed mode.

The Repeatable Read isolation level only sees data committed before the transaction began; it never sees either uncommitted data or changes committed by concurrent transactions during the transaction's execution. (However, each query does see the effects of previous updates executed within its own transaction, even though they are not yet committed.) This is a stronger guarantee than is required by the SQL standard for this isolation level, and prevents all of the phenomena described in Table 13.1 except for serialization anomalies. As mentioned above, this is specifically allowed by the standard, which only describes the minimum protections each isolation level must provide. This level is different from Read Committed in that a query in a repeatable read transaction sees a snapshot as of the start of the first non-transaction-control statement in the transaction, not as of the start of the current statement within the transaction. Thus, successive SELECT commands within a single transaction see the same data, i.e., they do not see changes made by other transactions that committed after their own transaction started. Applications using this level must be prepared to retry transactions due to serialization failures.

WIDELY AVAILABLE The Promise.all() static method takes an iterable of promises as input and returns a single Promise. This returned promise fulfills when all of the input's promises fulfill (including when an empty iterable is passed), with an array of the fulfillment values. It rejects when any of the input's promises rejects, with this first rejection reason. In this article Try it

Already fulfilled, if the iterable passed is empty. Asynchronously fulfilled, when all the promises in the given iterable fulfill. The fulfillment value is an array of fulfillment values, in the order of the promises passed, regardless of completion order. If the iterable passed is non-empty but contains no pending promises, the returned promise is still asynchronously (instead of synchronously) fulfilled. Asynchronously rejected, when any of the promises in the given iterable rejects. The rejection reason is the rejection reason of the first promise that was rejected. Description The Promise.all() method is one of the promise concurrency methods. It can be useful for aggregating the results of multiple promises. It is typically used when there are multiple related asynchronous tasks that the overall code relies on to work successfully — all of whom we want to fulfill before the code execution continues.

Promise.all() will reject immediately upon any of the input promises rejecting. In comparison, the promise returned by Promise.allSettled() will wait for all input promises to complete, regardless of whether or not one rejects. Use allSettled() if you need the final result of every promise in the input iterable. Like other promise combinators, Promise.all() immediately marks all promises as "handled" when it is called (by calling their .then() methods). Subsequent rejections after the first rejection will be ignored, and will not trigger any unhandledrejection events. Rejecting the returned promise does not cancel the remaining operations or unsubscribe the handlers attached to their promises. Repeatedly passing a long-lived pending promise to Promise.all() can accumulate handlers on that promise even when another input rejects each time.

value <any> A value with which the promise is fulfilled. options <Object> ref <boolean> Set to false to indicate that the scheduled Timeout should not require the Node.js event loop to remain active. Default: true. signal <AbortSignal> An optional AbortSignal that can be used to cancel the scheduled Timeout. const { setTimeout,

value <any> A value with which the promise is fulfilled. options <Object> ref <boolean> Set to false to indicate that the scheduled Immediate should not require the Node.js event loop to remain active. Default: true. signal <AbortSignal> An optional AbortSignal that can be used to cancel the scheduled Immediate. const { setImmediate,

value <any> A value with which the iterator returns. options <Object> ref <boolean> Set to false to indicate that the scheduled Timeout between iterations should not require the Node.js event loop to remain active. Default: true. signal <AbortSignal> An optional AbortSignal that can be used to cancel the scheduled Timeout between operations. const { setInterval,

The setImmediate(), setInterval(), and setTimeout() methods each return objects that represent the scheduled timers. These can be used to cancel the timer and prevent it from triggering. For the promisified variants of setImmediate() and setTimeout(), an AbortController may be used to cancel the timer. When canceled, the returned Promises will be rejected with an 'AbortError'. For setImmediate():

The <FileHandle> has to support writing. It is unsafe to use filehandle.writeFile() multiple times on the same file without waiting for the promise to be fulfilled (or rejected). If one or more filehandle.write() calls are made on a file handle and then a filehandle.writeFile() call is made, the data will be written from the current position till the end of the file. It doesn't always write from the beginning of the file.

mode <integer> Default: 0o666 flag <string> See support of file system flags. Default: 'w'. flush <boolean> If all data is successfully written to the file, and flush is true, filehandle.sync() is used to flush the data. Default: false. signal <AbortSignal> allows aborting an in-progress writeFile Returns: <Promise> Fulfills with undefined upon success.

Any specified <FileHandle> has to support writing. It is unsafe to use fsPromises.writeFile() multiple times on the same file without waiting for the promise to be settled. Similarly to fsPromises.readFile - fsPromises.writeFile is a convenience method that performs multiple write calls internally to write the buffer passed to it. For performance sensitive code consider using fs.createWriteStream() or filehandle.createWriteStream().