Javascript 如何用空字符串替换 undefined
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how to replace undefined with a empty string
提问by texas697
I am using jsPdf. When a field has been left blank "undefined" is printed on the pdf. I would like to replace that with a empty string. I am trying to use a if statement but I am not getting it.
我正在使用jsPdf。当一个字段留空时，“未定义”会打印在 pdf 上。我想用空字符串替换它。我正在尝试使用 if 语句，但我没有得到它。
doc.text(30, 190, "Budget : $");
if ($scope.currentItem.JobOriginalBudget == "undefined") {
doc.text(50, 190, " ");
}
else {
var y = '' + $scope.currentItem.JobOriginalBudget;
doc.text(50, 190, y);
};
采纳答案by apsillers
undefinedis a primitive value. Instead of comparing against the identifier undefined, you're comparing against the 9-character string"undefined".
undefined是一个原始值。您不是与 identifier 进行比较，而是undefined与 9 个字符的字符串" undefined"进行比较。
Simply remove the quotes:
只需删除引号：
if ($scope.currentItem.JobOriginalBudget == undefined)
Or compare against the typeofresult, which isa string:
或者与typeof结果进行比较，这是一个字符串：
if (typeof $scope.currentItem.JobOriginalBudget == "undefined")
回答by Nuno Costa
As per this answerI believe what you want is
根据这个答案，我相信你想要的是
doc.text(50, 190, $scope.currentItem.JobOriginalBudget || " ")
回答by theDarse
simply remove the "== 'undefined'"
只需删除“=='未定义'”
if (!$scope.currentItem.JobOriginalBudget) {
doc.text(50, 190, " ");
}
回答by Abdullah Pariyani
var ab = {
firstName : undefined,
lastName : undefined
}
let newJSON = JSON.stringify(ab, function (key, value) {return (value === undefined) ? "" : value});
console.log(JSON.parse(newJSON))<p>
<b>Before:</b>
let ab = {
firstName : undefined,
lastName : "undefined"
}
<br/><br/>
<b>After:</b>
View Console
</p>回答by Maxime
If item is an Object use, this function :
如果 item 是 Object 使用，则此函数：
replaceUndefinied(item) {
var str = JSON.stringify(item, function (key, value) {return (value === undefined) ? "" : value});
return JSON.parse(str);
}
