問(wèn)題描述
HTML頁(yè)面:
<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>xhr</title>
</head>
<body>
<script>
var xhr_test = new XMLHttpRequest();
xhr_test.open("GET","xhrtest",true);
xhr_test.send();
alert(xhr_test.responseText);
</script>
</body>
</html>
main.py 文件:
The main.py file:
import webapp2
from handlers import cookies,pages
application = webapp2.WSGIApplication([
('/xhr',pages.XHR),
('/xhrtest', cookies.XHRTest)
],
debug=True)
請(qǐng)求處理程序:
class XHRTest(webapp2.RequestHandler):
def get(self):
self.response.write('0')
和，
class XHR(webapp2.RequestHandler):
def get(self):
f = open('static/html/xhr.html','r')
self.response.write(f.read())
現(xiàn)在，當(dāng)我點(diǎn)擊 URL localhost:8080/xhrtest 時(shí)，瀏覽器會(huì)立即將響應(yīng) 0 顯示為頁(yè)面內(nèi)容.
Now, when I hit upon the url localhost:8080/xhrtest the browser promptly shows the response 0 as the page's content.
點(diǎn)擊url localhost:8080/xhr間接點(diǎn)擊/xhrtest，在alert框中彈出一個(gè)空字符串(responseText是一個(gè)空字符串)但是檢查在network標(biāo)簽下chrome的response標(biāo)簽，可以看到請(qǐng)求的響應(yīng)是0.
Hitting the url localhost:8080/xhr which indirectly hits /xhrtest, pops up an empty string in the alert box (the responseText is an empty string) but checking chrome's response tab under the network tab, I can see that the request's response is 0.
那么為什么 xhr_test.responseText 不能顯示相同的響應(yīng)?
So why is xhr_test.responseText not able to display the same response?
推薦答案
send 調(diào)用是異步的(您已將 'async' 參數(shù)設(shè)置為 true)，這意味著您的警報(bào)會(huì)在請(qǐng)求完成之前立即發(fā)生.您應(yīng)該向 xhr.onreadystatechange 添加一個(gè)事件偵聽(tīng)器并在其中使用響應(yīng).
The call to send is asynchronous (you've set the 'async' parameter to true), which means that your alert is happening immediately, before the request finishes.
You should add an event-listener to xhr.onreadystatechange and use the response within that.
將true"更改為false"可以使這個(gè)簡(jiǎn)單的示例工作，但在一般情況下不是一個(gè)好主意.
Changing the 'true' to 'false' would make this simple example work, but is not a good idea in the general case.
Ajax 上的 MDN 頁(yè)面解釋了如何使用 XMLHttpRequest.
The MDN page on Ajax explains how XMLHttpRequest should be used.
這篇關(guān)于XHR responseText 是空字符串的文章就介紹到這了，希望我們推薦的答案對(duì)大家有所幫助，也希望大家多多支持html5模板網(wǎng)！