javascript: plus symbol before variable
this really sounds like a simple question but I had no luck searching. what does the +d in
function addMonths(d, n, keepTime) {
if (+d) {
means?
The + operator returns the numeric representation of the object. So in your particular case, it would appear to be predicating the if on whether or not d is a non-zero number.
Reference here. And, as pointed out in comments, here.
It is a unary "+" operator which yields a numeric expression. It would be the same as d*1 , I believe.
As explained in other answers it converts the variable to a number. Specially useful when d can be either a number or a function that evaluates to a number.
Example (using the addMonths function in the question):
addMonths(function(){return x*y;}, 1, true);
addMonths(34,1,true);
addMonths("34",1,true);
then the +d will evaluate to a number in all cases. Thus avoiding the need to check for the type and take different code paths depending on whether d is a number, a function or a string that can be converted to a number.
下一篇: javascript：在变量前加上符号