Higher order functions returning anything but a non-boolean is questionable. Why?

问题

function each(collection, callback) {
  var arr = [];
  for(var i = 0; i < collection.length; i++) {
      var result = callback(collection[i])
      if (typeof result !== 'undefined') {
        arr.push(callback(collection[i]));
      }
    }
  return arr
}

function isNumber(item) {
    if (typeof item === "number") {
      return item * 2;
    }
}

I am trying to understand higher order functions. The above works, but is apparently not best practice to return a value with isNumber. I have been told that a Boolean value should be returned. Why? It works.

Update: It appears to be because of the function name! Thanks everyone I just thought there might be some technical reason

回答1:

If a function is called isNumber, it should return a boolean.

Also, your each function is a map not an each. In that case your code should probably look like.

function flatMap(collection, callback) {
  var arr = [];
  for(var i = 0; i < collection.length; i++) {
      var result = callback(collection[i])
      if (typeof result !== 'undefined') {
        arr.push(callback(collection[i]));
      }
    }
  return arr;
}

function times2(item) {
    if (typeof item === "number") {
      return item * 2;
    }
    return item;
}

map([1,2,3,"hello"], times2);

If you wanted iteration that can be stopped, then it would look like

function iterate(collection, callback) {
  for(var i = 0; i < collection.length; i++) {
    var result = callback(collection[i])
    if (typeof result === false) {
      return;
    }
  }
}

function doSomethingAndStopIfNotANumber(item) {
   console.log(item);
   return typeof item == "number";
}

iterate([1,2,3, "hello", 4, 5], doSomethingAndStopIfNotANumber);

Note that Array.prototype.forEach does not allow you to stop iteration by returning false, for that you'd need to misuse Array.prototype.every (because that function returns a boolean, so it's just a semantic problem, not like map where you build an array and throw it away) or write a function like I did above.

来源：https://stackoverflow.com/questions/37861822/higher-order-functions-returning-anything-but-a-non-boolean-is-questionable-why

标签

javascript

boolean

higher-order-functions