javascript book "eloquent javascript"
function negate(func) {
return function(x) {
return !func(x);
};
}
var isNotNaN = negate(isNaN);
show(isNotNaN(NaN));
someone explain it and as title of question says what is higher-order function, what does this code do ?
When most people think of functions they accept objects or values as parameters and similarly return an object or value, such as function addTwoNumbers(int x, int y).
In mathematics and computer science, a "higher-order function" is just like any other function, except that in addition to arguments that are values it can also accept a function as an argument.
...that's all a higher-order function is, really :)
In the example you posted, negate is a higher-order function because it has a parameter func which is a function (or rather, assigned to a function).
negate goes further: it doesn't merely call func and negate its result, instead it returns an anonymous function (that's the inner return function(x) bit).
So the isNotNaN variable then has the type (and value) of that earlier anonymous function.
Higher-order function is a function that:
What does your code do? it negates the function isNan (to isNotNan). It accept a function (isNan), and then output the negation (isNotNan). It's just that simple.
