There's currently no way to wait for a condition except with WaitFunc and a selector #680
Comments
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FWIW, puppeteer has https://devdocs.io/puppeteer/index#pagewaitforfunctionpagefunction-options-args |
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There should be something like the puppeteer API |
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@opennota It seems that you just want the wait part of Lines 161 to 166 in e297055 Borrow this implementation, your code can be changed to (I have extended it to be runnable, and it's based on package main
import (
"context"
"fmt"
"log"
"net/http"
"net/http/httptest"
"time"
"github.com/chromedp/chromedp"
)
func main() {
ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
fmt.Fprint(w, `
<html>
<script>
let v = 0;
setTimeout(()=>{v = 100}, 1000);
</script>
<body>
hello world
</body>
</html>
`)
}))
defer ts.Close()
ctx, cancel := chromedp.NewContext(context.Background(), chromedp.WithDebugf(log.Printf))
defer cancel()
ctx, cancel = context.WithTimeout(ctx, 5*time.Second)
defer cancel()
if err := chromedp.Run(ctx,
chromedp.Navigate(ts.URL),
chromedp.ActionFunc(func(ctx context.Context) error {
for {
select {
case <-ctx.Done():
return ctx.Err()
// you can customize the interval below
case <-time.After(5 * time.Millisecond):
}
var result bool
err := chromedp.Evaluate(`v === 100`, &result).Do(ctx)
if err != nil {
return err
}
if result {
return nil
}
}
}),
); err != nil {
log.Fatal(err)
}
}The problem of this implementation is that it involves many roundtrips on the WebSocket connection. I have looked into the implementation of https://devdocs.io/puppeteer/index#pagewaitforfunctionpagefunction-options-args, and found that the wait part is totally happens in the browser, and there is just one roundtrip on the WebSocket connection. The following implementation is borrowed from https://devdocs.io/puppeteer/index#pagewaitforfunctionpagefunction-options-args (It uses Runtime.callFunctionOn and requires an package main
import (
"context"
"encoding/json"
"fmt"
"log"
"net/http"
"net/http/httptest"
"github.com/chromedp/cdproto/cdp"
"github.com/chromedp/cdproto/runtime"
"github.com/chromedp/chromedp"
)
func main() {
ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
fmt.Fprint(w, `
<html>
<script>
let v = 0;
setTimeout(()=>{v = 100}, 3000);
</script>
<body>
hello world
</body>
</html>
`)
}))
defer ts.Close()
ctx, cancel := chromedp.NewContext(context.Background(), chromedp.WithDebugf(log.Printf))
defer cancel()
// copied from puppeteer
waitForPredicatePageFunction := `async function waitForPredicatePageFunction(predicateBody, polling, timeout, ...args) {
const predicate = new Function('...args', predicateBody);
let timedOut = false;
if (timeout)
setTimeout(() => (timedOut = true), timeout);
if (polling === 'raf')
return await pollRaf();
if (polling === 'mutation')
return await pollMutation();
if (typeof polling === 'number')
return await pollInterval(polling);
/**
* @returns {!Promise<*>}
*/
async function pollMutation() {
const success = await predicate(...args);
if (success)
return Promise.resolve(success);
let fulfill;
const result = new Promise((x) => (fulfill = x));
const observer = new MutationObserver(async () => {
if (timedOut) {
observer.disconnect();
fulfill();
}
const success = await predicate(...args);
if (success) {
observer.disconnect();
fulfill(success);
}
});
observer.observe(document, {
childList: true,
subtree: true,
attributes: true,
});
return result;
}
async function pollRaf() {
let fulfill;
const result = new Promise((x) => (fulfill = x));
await onRaf();
return result;
async function onRaf() {
if (timedOut) {
fulfill();
return;
}
const success = await predicate(...args);
if (success)
fulfill(success);
else
requestAnimationFrame(onRaf);
}
}
async function pollInterval(pollInterval) {
let fulfill;
const result = new Promise((x) => (fulfill = x));
await onTimeout();
return result;
async function onTimeout() {
if (timedOut) {
fulfill();
return;
}
const success = await predicate(...args);
if (success)
fulfill(success);
else
setTimeout(onTimeout, pollInterval);
}
}
}
`
var exeCtxID runtime.ExecutionContextID
// run
if err := chromedp.Run(ctx,
chromedp.Navigate(ts.URL),
// to get the runtime.ExecutionContextID
chromedp.Query("random-selector",
func(s *chromedp.Selector) {
chromedp.WaitFunc(func(ctx context.Context, cur *cdp.Frame, id runtime.ExecutionContextID, ids ...cdp.NodeID) ([]*cdp.Node, error) {
exeCtxID = id
return []*cdp.Node{}, nil
})(s)
},
chromedp.AtLeast(0),
),
chromedp.ActionFunc(func(ctx context.Context) error {
predicateBody, err := json.Marshal(`return (()=>v === 100)(...args);`)
if err != nil {
return err
}
timeout, err := json.Marshal(5000)
if err != nil {
return err
}
polling, err := json.Marshal("raf")
if err != nil {
return err
}
// I just ignore the result below. It should parsed to check whether it's timeout
_, _, err = runtime.CallFunctionOn(waitForPredicatePageFunction).
WithExecutionContextID(exeCtxID).
WithReturnByValue(false).
WithAwaitPromise(true).
WithUserGesture(true).
WithArguments([]*runtime.CallArgument{
{Value: predicateBody},
{Value: polling},
{Value: timeout},
}).Do(ctx)
return err
}),
); err != nil {
log.Fatal(err)
}
} |
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This issue should have been addressed by #766. Please file a new issue if you find bugs in that feature. Thank you! |
What I want is to evaluate some JS repeatedly until it returns the expected result. There seems to be no other way to do that but with a clumsy code like this, using
WaitFuncand a random selector:It would be great if one could wait for a JS condition using a simpler action.
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