Javascript数组值未定义...我该如何测试 [英] Javascript array value is undefined ... how do I test for that
问题描述
我正在尝试测试是否未定义Javascript变量。
I am trying to test to see whether a Javascript variable is undefined.
您将看到我不期望predQuery [preId]的值为'未定义'如果我没有首先得到警告说它令人难以置信。但我经常这样做,所以我猜我的陈述
You will see that I am not expecting the value of predQuery[preId] to be 'undefined' if I don't first get an alert saying "its unbelievable". But I often do, so I am guessing that my statement
predQuery[preId]=='undefined')
未正确匹配未定义的元素。
is not matching the undefined elements properly.
if((predQuery.length < preId) || (predQuery[preId]=="") || (predQuery[preId]=='undefined')){
alert("its unbelievable");
alert(predQuery[preId]);
queryPreds[variables] = preId;
queryObjs[variables] = objId;
predQuery[preId] = variables;
}
else {
alert(predQuery[preId]);
var predIndex = predQuery[preId];
queryPreds[predIndex] = preId;
queryObjs[predIndex] = objId;
}
如果需要,我可以添加更多代码。
I can add more code if needed.
推荐答案
array [index] =='undefined'
比较值字符串undefined的数组索引。
你可能正在寻找 typeof array [index] =='undefined'
,它比较了类型。
array[index] == 'undefined'
compares the value of the array index to the string "undefined".
You're probably looking for typeof array[index] == 'undefined'
, which compares the type.
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