The unary operators + and - can be used to convert some value types to numeric values.
But not every value can be converted to a Number type: use it with an object, and result will be always NaN (Not A Number).
var obj = {x : 1};
doSomethingWithNumber(+obj); // Noncompliant
function foo(){
return 1;
}
doSomethingWithNumber(-foo); // Noncompliant
var obj = {x : 1};
doSomethingWithNumber(+obj.x);
function foo(){
return 1;
}
doSomethingWithNumber(-foo());
var str = '42';
doSomethingWithNumber(+str);
Unary + and - can be used with objects corresponding to primitive types.
var b = new Boolean(true); doSomethingWithNumber(-b); // Compliant