Why I can't assign the "th" variant in this JS function?
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I want to get JSON data from the Internet,and I write a js function to load the JSON data to my ListModel.But there is an unexpected error, which is ,var "th" can't be assigned in onreadystatechange function.What happened?
Here is the function:
function getPictureURLByID(idstr){
var beforeID = "http://ting.baidu.com/data/music/links?songIds=";
var sea = beforeID + idstr; // "idstr" is a id string that I get from another JS function,such like:2152968,107184439,91590745,...
var th = "";var here = new XMLHttpRequest(); here.open("GET",sea); here.onreadystatechange=function(){ if (here.readyState == XMLHttpRequest.DONE){ var there = JSON.parse(here.responseText); th = there.data.songList[0].songPicSmall; //"th" is assigned to the URL of certain image console.log(th); // this prints something like :http://a.hiphotos.baidu.com/ting/pic/item/cdbf6c81800a19d80b7d421131fa828ba61e46ac.jpg } } here.send(); console.log(th); //while this prints nothing,just an empty string return th;}
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You should exercise some patience. Typical rule in the past was to wait at least a day or a couple of them.
Unfortunately, I cannot help you with this. Possibly a stupid question, can't you use a debugger?
In C++ I would simply set a break point around and check if the program code is executed as expected. -
I agree with @koahnig . Be patient.
Regarding your question, XMLHttpRequest performs an asynchronous request. "th" is empty right after send() because onreadystatechange wasn't triggered yet. You'd better have a callback function.
function getTh(onThReady){ var here = new XMLHttpRequest(); here.open("GET",sea); here.onreadystatechange=function(){ if (here.readyState == XMLHttpRequest.DONE){ var there = JSON.parse(here.responseText); onThReady(there.data.songList[0].songPicSmall); } } here.send(); } ... getTh(function(th){ console.log(th); });