用JavaScript中的`if`语句连接字符串 [英] Concatenating strings with `if` statements in JavaScript
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问题描述
我正在尝试设置一个脚本来连接字符串中的一些变量(如果它们存在),以便将相应的元数据标记放入呈现的HTML文档中。
I'm attempting to set up a script to concatenate some variables inside a string if they exist, in order to place the appropriate metadata tags into a rendered HTML document.
我的串联代码是:
data = "<html>\n<head>\n" + "</head>\n<body>\n\n" + paras.join("\n\n") + "\n\n</body>\n</html>";
我正在尝试添加 if
语句如下所示(第一项和第二项之间):
I'm trying to add if
statements like the following into it (between the first and second items):
if (typeof metadata_title !== "undefined") {
"<title>" + metadata_title + "</title>\n"
}
if (typeof metadata_author !== "undefined") {
"<meta name=\"author\" content=\"" + metadata_author + "\"></meta>\n"
}
if (typeof metadata_date !== "undefined") {
"<meta name=\"date\" content=\"" + metadata_date + "\"></meta>\n"
}
但是我无法将这些语句直接添加到连接代码中(它会抛出错误:意外的令牌(
)。
But I can't add any of these statements directly into the concatenation code (it throws an error: Unexpected token (
).
我最好如何将这些语句添加到我的串联字符串中?
How best would I go about adding statements such as these into my concatenation string?
推荐答案
我使用三元运算符:
data = "<html>\n"
+ "<head>\n"
+ ( typeof metadata_title !== "undefined" ? "<title>" + metadata_title + "</title>\n" : "" )
+ ( typeof metadata_author !== "undefined" ? "<meta name=\"author\" content=\"" + metadata_author + "\"></meta>\n" : "" )
+ ( typeof metadata_date !== "undefined" ? "<meta name=\"date\" content=\"" + metadata_date + "\"></meta>\n" : "" )
+ "</head>\n"
+ "<body>\n"
+ "\n"
+ paras.join("\n\n")
+ "\n"
+ "\n"
+ "</body>\n"
+ "</html>"
;
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