casperjs timeout issue with an endless loop

Question

casperjs timeout issue with an endless loop

Currently, I am utilizing casperjs to retrieve the content of a website that updates its values using websockets. Rather than attaching an event listener to each value, my goal is to scrape the entire website every 10 seconds.

Here is the code snippet I am using:

casper.waitForResource("http://website.com", function() {
    getPrices(casper);
});

Within the getPrices function, I successfully extract the values and end with the following lines of code:

setTimeout(getPrices(casper), 5000);

The issue I am facing is that Casper appears to be disregarding the timeout and executing without delay. Additionally, I am concerned about the recursive nature of this solution potentially leading to a memory stack overflow in the long term.

Could anyone provide guidance on how to achieve this task more effectively?

Thank you!

javascript phantomjs casperjs slimerjs

Answer 1

Answer №1

The issue lies in your code where you are invoking the getPrices(casper) function immediately and then passing its return value to the setTimeout() method, causing it to not wait for the timer to trigger before executing the function.

This can be better explained through the following comparison:

setTimeout(getPrices(casper), 5000);

can be likened to:

var temp = getPrices(casper);
setTimeout(temp, 5000);

As evident here, the function is being called right away and its return value is passed to setTimeout(), which may not be the desired behavior.

To resolve this issue, you should consider using one of these methods:

// Utilize an anonymous stub function
setTimeout(function() {
    getPrices(casper);
}, 5000);

// Use .bind() method to create a temporary function with the casper parameter bound to it
setTimeout(getPrices.bind(null, casper), 5000);

Note that calling a function repeatedly from within a setTimeout() does not result in true recursion. The call stack completely unwinds prior to the execution of setTimeout(), preventing any accumulation of stack frames.

Answer 2

The issue lies in your code where you are invoking the getPrices(casper) function immediately and then passing its return value to the setTimeout() method, causing it to not wait for the timer to trigger before executing the function.

This can be better explained through the following comparison:

setTimeout(getPrices(casper), 5000);

can be likened to:

var temp = getPrices(casper);
setTimeout(temp, 5000);

As evident here, the function is being called right away and its return value is passed to setTimeout(), which may not be the desired behavior.

To resolve this issue, you should consider using one of these methods:

// Utilize an anonymous stub function
setTimeout(function() {
    getPrices(casper);
}, 5000);

// Use .bind() method to create a temporary function with the casper parameter bound to it
setTimeout(getPrices.bind(null, casper), 5000);

Note that calling a function repeatedly from within a setTimeout() does not result in true recursion. The call stack completely unwinds prior to the execution of setTimeout(), preventing any accumulation of stack frames.

casperjs timeout issue with an endless loop

Answer №1

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