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Taken from the underscore.js source:
_.isNaN = function(obj) {
return _.isNumber(obj) && obj != +obj;
};
Why did they do it this way? Is the above implementation equivalent to:
_.isNaN = function(obj) {
return obj !== obj;
};
If it is, why the "more complicated" version? If it is not, what are the behavioural differences?
673
The isNaN() function is used to check whether a given value is an illegal number or not. It returns true if value is a NaN else returns false. It is different from the Number. isNaN() Method.
1. isNaN() Method: To determine whether a number is NaN, we can use the isNaN() function. It is a boolean function that returns true if a number is NaN otherwise returns false.
isNaN() method returns true if the value is NaN , and the type is a Number.
isNaN converts the argument to a Number and returns true if the resulting value is NaN . Number. isNaN does not convert the argument; it returns true when the argument is a Number and is NaN .
_.isNaN(new Number(NaN)) returns true.
And that's by design.
var n = new Number(NaN);
console.log(_.isNaN(n), n!==n); // logs true, false
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