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PHP ?? ?? ????? AJAX ?? ??

AJAX? ?? ??? ??? ????.

68.png

1. ???? ?????. ????? oclick ???, onchange ???? ????. , onkeyup ??? ?

??:

oclick ???: ??? ??? ? ??

onchange ???: ??? ??? ??? ? ??

onkeyup ???: ??? ?? ??? ? ??

2. XMLHttpRequest ?? ??

???? ??? ??? ??? ??? ???? ???. Conventional ??? ??? ? ???? ??? ??? ????

XMLHttpRequest ??? open() ? send() ???? ???? ??? ??? ????

var xmlhttp;
if (window.XMLHttpRequest)
  {// code for IE7+, Firefox, Chrome, Opera, Safari
  xmlhttp=new XMLHttpRequest();
  }
else
  {// code for IE6, IE5
  xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
  }
??: ?? ??? ?????. ???? ??? ??? ????.

4. , ??? ???? ???? ????? ?????.

??? ??? ???? ? ?? ?? ?? ??? ???? ???.

69.png

readyState? ??? ??? onreadystatechange ???? ??????.

readyState ??? XMLHttpRequest? ?? ??? ?????. XMLHttpRequest ??? ? ?? ??? ??? ??? ????.

onreadystatechange ????? ?? ????? ?????. ??? ?????. ??? ??? ??? ? ???? ?????.

?. ReadyState? 4?? ??? 200?? ??? ?????? ?????.

??: onreadystatechange ???? ? ReadyState ??? ?? 5?(0~4) ??????


????? ??? ???? XMLHttpRequest ??? responseText ?? responseXML ??? ??? ? ????.

67.png

?: 

    xmlhttp.open("GET","test1.txt",true);
    xmlhttp.send();

66.png

5. js? ???? ??? ???? ???? ???? ???????.

js? ??? ?? ?? ??? ??? ?????. id? ??? XMLHttpRequest ??? ??? ???? ????.

???? ??
||
var xmlhttp; if (window.XMLHttpRequest) {// code for IE7+, Firefox, Chrome, Opera, Safari xmlhttp=new XMLHttpRequest(); } else {// code for IE6, IE5 xmlhttp=new ActiveXObject("Microsoft.XMLHTTP"); }