JavaScript higher-order functions

Examples

Functions that operate on other functions, either by taking them as arguments or by returning them, are called higher-order functions. They allow us to abstract over actions as well as values. There are several types, here are some examples.

Functions that create new functions

function greaterThan(n) {
  return m => m > n;
}
let greaterThan10 = greaterThan(10);
console.log(greaterThan10(11));

Functions that change other functions

function noisy(f) {
  return (...args) => {
    console.log("calling with", args);
    let result = f(...args);
    console.log("called with", args, ", returned", result);
    return result;
  };
}
noisy(Math.min)(3, 2, 1);

Functions that provide new types of flow control

function unless(test, then) {
  if (!test) then();
}
 
repeat(3, n => {
  unless(n % 2 == 1, () => {
    console.log(n, "is even");
  });
});

ES6

Funciton properties

1. name

   The name property contains the function’s name:

   function foo() {};
   console.log(foo.name); // foo
    
   let func1 = function () {};
   console.log(func1.name); // func1
    
   let func4;
   func4 = function () {};
   console.log(func4.name); // func4

   1. Default values

      let [func1 = function () {}] = [];
      console.log(func1.name); // func1
       
      let { f2: func2 = function () {} } = {};
      console.log(func2.name); // func2
       
      function g(func3 = function () {}) {
          return func3.name;
      }
      console.log(g()); // func3