how we can use evaluateAsync in phantomjs

问题

what's the usage of evaluateAsync and when we have to use this function and what's the benefit of using this function . in the below we see a poor documentation for this :

var webPage = require('webpage');
var page = webPage.create();
// @TODO: Finish page.evaluateJavaScript example.

any body can show a example of usage of evaluateAsync in phantomjs

回答1:

This function allows you to execute any JavaScript code like the evaluate API function. But it will evaluate your code asynchronous. It means:

• Current execution context will not be blocked.
• It will not return any result.

Let's say you want execute some long-running JavaScript code, but you don't interested in its result. If you will use evaluate, your current execution context will be blocked.

The documentation for evaluateAsync is a bit wrong. The correct signature for evaluateAsync is: evaluateAsync(function, ms, args), where:

• function - the function to evaluate
• ms - time to wait before execution
• args - function arguments

Example:

evaluateAsync(function() {
   console.log('Hi! I\'m evaluateAsync call!');
}, 1000);

Using in the real world:

• You want to capture some asynchronous events.
• Unit testing! AFAIK, PhantomJS runners use evaluateAsync to run unit tests.

来源：https://stackoverflow.com/questions/22474525/how-we-can-use-evaluateasync-in-phantomjs