虽然默认参数没有重载，但它可能解决开发人员在这方面面临的一些问题。输入是严格由顺序决定的，你不能重新排序，因为你希望在经典重载:

function transformer(
    firstNumber = 1,
    secondNumber = new Date().getFullYear(),
    transform = function multiply(firstNumber, secondNumber) {
        return firstNumber * secondNumber;
    }
) {
    return transform(firstNumber, secondNumber);
}

console.info(transformer());
console.info(transformer(8));
console.info(transformer(2, 6));
console.info(transformer(undefined, 65));

function add(firstNumber, secondNumber) {
    return firstNumber + secondNumber;
}
console.info(transformer(undefined, undefined, add));
console.info(transformer(3, undefined, add));

结果(2020年):

2020
16160
12
65
2021
2023

更多信息:https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Default_parameters

我们用over.js来解决这个问题是一种非常优雅的方式。你可以:

var obj = {

  /**
   * Says something in the console.
   *
   * say(msg) - Says something once.
   * say(msg, times) - Says something many times.
   */
  say: Over(
    function(msg$string){
      console.info(msg$string);
    },
    function(msg$string, times$number){
      for (var i = 0; i < times$number; i++) this.say(msg$string);
    }
  )

};

多年来，我一直在使用这个函数来美化我的重载:

function overload(){
  const fs = arguments, fallback = fs[fs.length - 1];
  return function(){
    const f = fs[arguments.length] || (arguments.length >= fs.length ? fallback : null);
    return f.apply(this, arguments);
  }
}

型:

function curry1(f){
  return curry2(f, f.length);
}

function curry2(f, minimum){
  return function(...applied){
    if (applied.length >= minimum) {
      return f.apply(this, applied);
    } else {
      return curry2(function(...args){
        return f.apply(this, applied.concat(args));
      }, minimum - applied.length);
    }
  }
}

export const curry = overload(null, curry1, curry2);

看看jQuery的off方法:

  function off( types, selector, fn ) {
    var handleObj, type;
    if ( types && types.preventDefault && types.handleObj ) {

        // ( event )  dispatched jQuery.Event
        handleObj = types.handleObj;
        jQuery( types.delegateTarget ).off(
            handleObj.namespace ?
                handleObj.origType + "." + handleObj.namespace :
                handleObj.origType,
            handleObj.selector,
            handleObj.handler
        );
        return this;
    }
    if ( typeof types === "object" ) {

        // ( types-object [, selector] )
        for ( type in types ) {
            this.off( type, selector, types[ type ] );
        }
        return this;
    }
    if ( selector === false || typeof selector === "function" ) {

        // ( types [, fn] )
        fn = selector;
        selector = undefined;
    }
    if ( fn === false ) {
        fn = returnFalse;
    }
    return this.each( function() {
        jQuery.event.remove( this, types, fn, selector );
    } );
  }

许多重载函数在优化性能时几乎不可读。你必须破译函数的头部。这可能比使用我提供的重载函数更快;但是，从人的角度来看，它在识别调用了哪个重载方面要慢一些。

我经常这样做:

C#:

public string CatStrings(string p1)                  {return p1;}
public string CatStrings(string p1, int p2)          {return p1+p2.ToString();}
public string CatStrings(string p1, int p2, bool p3) {return p1+p2.ToString()+p3.ToString();}

CatStrings("one");        // result = one
CatStrings("one",2);      // result = one2
CatStrings("one",2,true); // result = one2true

JavaScript相当于:

function CatStrings(p1, p2, p3)
{
  var s = p1;
  if(typeof p2 !== "undefined") {s += p2;}
  if(typeof p3 !== "undefined") {s += p3;}
  return s;
};

CatStrings("one");        // result = one
CatStrings("one",2);      // result = one2
CatStrings("one",2,true); // result = one2true

This particular example is actually more elegant in javascript than C#. Parameters which are not specified are 'undefined' in javascript, which evaluates to false in an if statement. However, the function definition does not convey the information that p2 and p3 are optional. If you need a lot of overloading, jQuery has decided to use an object as the parameter, for example, jQuery.ajax(options). I agree with them that this is the most powerful and clearly documentable approach to overloading, but I rarely need more than one or two quick optional parameters.

编辑:根据Ian的建议更改IF测试

用形参重载函数的最好方法不是检查实参长度或类型;检查类型只会让你的代码变慢，你可以享受数组、空值、对象等的乐趣。

大多数开发人员所做的是将一个对象作为方法的最后一个参数。这个物体可以装任何东西。

function foo(a, b, opts) {
  // ...
  if (opts['test']) { } //if test param exists, do something.. 
}


foo(1, 2, {"method":"add"});
foo(3, 4, {"test":"equals", "bar":"tree"});

然后你可以在你的方法中任意处理它。[开关，if-else，等等]

我不确定最佳实践，但我是这样做的:

/*
 * Object Constructor
 */
var foo = function(x) {
    this.x = x;
};

/*
 * Object Protoype
 */
foo.prototype = {
    /*
     * f is the name that is going to be used to call the various overloaded versions
     */
    f: function() {

        /*
         * Save 'this' in order to use it inside the overloaded functions
         * because there 'this' has a different meaning.
         */   
        var that = this;  

        /* 
         * Define three overloaded functions
         */
        var f1 = function(arg1) {
            console.log("f1 called with " + arg1);
            return arg1 + that.x;
        }

        var f2 = function(arg1, arg2) {
             console.log("f2 called with " + arg1 + " and " + arg2);
             return arg1 + arg2 + that.x;
        }

        var f3 = function(arg1) {
             console.log("f3 called with [" + arg1[0] + ", " + arg1[1] + "]");
             return arg1[0] + arg1[1];
        }

        /*
         * Use the arguments array-like object to decide which function to execute when calling f(...)
         */
        if (arguments.length === 1 && !Array.isArray(arguments[0])) {
            return f1(arguments[0]);
        } else if (arguments.length === 2) {
            return f2(arguments[0], arguments[1]);
        } else if (arguments.length === 1 && Array.isArray(arguments[0])) {
            return f3(arguments[0]);
        }
    } 
}

/* 
 * Instantiate an object
 */
var obj = new foo("z");

/*
 * Call the overloaded functions using f(...)
 */
console.log(obj.f("x"));         // executes f1, returns "xz"
console.log(obj.f("x", "y"));    // executes f2, returns "xyz"
console.log(obj.f(["x", "y"]));  // executes f3, returns "xy"