Javascript 变量前加号的用途是什么？
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What is the purpose of a plus symbol before a variable?
提问by goh
this really sounds like a simple question but I had no luck searching. what does the +din
这真的听起来像一个简单的问题，但我没有运气搜索。+din是什么意思
function addMonths(d, n, keepTime) {
if (+d) {
means?
方法？
回答by Paul Sonier
回答by naivists
It is a unary "+" operator which yields a numeric expression. It would be the same as d*1, I believe.
它是一个一元“+”运算符，它产生一个数字表达式。d*1我相信，这将与 相同。
回答by RubenLaguna
As explained in other answers it converts the variable to a number. Specially useful when d can be either a number or a string functionthat evaluates to a number.
如其他答案中所述，它将变量转换为数字。当 d 可以是数字或字符串时特别有用功能计算结果为一个数字。
Example (using the addMonthsfunction in the question):
示例（使用问题中的addMonths函数）：
addMonths(34,1,true);
addMonths("34",1,true);
then the +dwill evaluate to a number in all cases. Thus avoiding the need to check for the type and take different code paths depending on whether dis a number, a function or a string that can be converted to a number.
那么+d在所有情况下都将评估为一个数字。从而避免需要检查类型并根据d是数字、函数还是可以转换为数字的字符串采用不同的代码路径。
