Ajax访问JSON（备忘）

(function() {  
    var createRequest = function() {  
        var request;  
        try { //support IE7+, Firefox, Chrome, Safari and Opera.  
            request = new XMLHttpRequest();  
        } catch(tryMS) {  
            try {  
                request = new ActiveXObject("Msxml2.XMLHTTP");  
            } catch(otherMS) {  
                try { // support IE6 and IE5  
                    request = new ActiveXObject("Microsoft.XMLHTTP");  
                } catch(failed) {  
                    request = null;  
                }  
            }  
        }  
        return request;  
    }  
      
    var checkText = function() {  
        var request = createRequest();  
        var obj = this;  
        if(request === null) {  
            alert("Unable to create request!");  
        } else {  
            var url = "json/test.json?id=" + Math.random();  
            request.onreadystatechange = function() {  
                if(request.readyState == 4 && request.status == 200) {  
                    var json = JSON.parse(request.responseText),  
                        text = obj.value;  
                    document.getElementById("prompt").innerHTML = json[text];  
                }  
            }  
            request.open("GET", url, true);  
            request.send(null);  
        }  
    }  
      
    document.getElementById("text").onkeyup = checkText;  
})();  
  
  
\\------------jquery  
  
  
$(function() {  
    $("#text").keyup(function() {  
        var $domText = $(this);  
        $.ajax( {  
            async: true,  
            cache: false,  
            type: "get",  
            url: "json/test.json",  
            dataType: "json",  
            success: function(data) {  
                $("#prompt").html(data[$domText.val()]);  
            }  
        });  
    });  
});