如何选择在函数中将变量分配给哪个参数？ -Javascript

Question

赋予正常功能；

function descriptions(awesome, cool, alright){
   return (awesome || "no one") + " is awesome. " + cool + " is cool. " +
     + alright + " is alright";
}
descriptions("jane", "jack", "jefferson");
//returns "jane is awesome. jack is cool. jefferson is alright."

我想使用相同的函数，但只想将最后两个参数传递给它，如下所示：

descriptions(cool : "john", alright : "jane"); //I would like a statement similar to this that works.
//should return "no one is awesome. jack is cool. jefferson is alright."

以上将如何完成？

Answer 1

使用对象解构可以实现语法上不同但语义上相似的某些功能

function descriptions({ awesome = 'no one', cool, alright }) {
    return awesome + " is awesome. " + cool + " is cool. " +
     + alright + " is alright";
}

然后，您只需使用具有相应属性的对象来调用它：

descriptions({ cool: 'a', alright: 'b'});

Answer 2

在任何各种ECMAScript（包括JavaScript）中都是不可能的。

从理论上讲，可以做一些使用条件自定义逻辑的事情：

function(a,b,c){
   if(arguments.length === 1) {
      // we're in object mode;
      b = a.b
      c = a.c
      a = a.a || 'default';
   }
}

但这不是语言的一部分。

这是不可能的，例如：

function foo(a,b,c){return a/(b || 1) + c;}
foo({c:1,b:2,a:3})

也可以根据参数数量有条件地定义值：

function say (a,b,c) {
   if(arguments.length === 2) {
      c = b;
      b = a;
      a = 'cat';
   }
   console.log('a ' + a + ' likes a ' + b + ' and a ' + c)
}
say('dog', 'bone', 'walk') // a dog likes a bone and a walk
say('mouse', 'bowl of milk') // a cat likes a mouse and a bowl of milk

Answer 3

是的，您当然可以实现！ 如果没有提供变量，您可以使用许多开发人员使用的巧妙技巧将变量设置为默认值。

function descriptions(awesome, cool, alright){
awesome = awesome || "";
if (awesome === "")
{
    return "no one" + " is awesome. " + cool + " is cool. " +
 + alright + " is alright";
}
else{
    return awesome + " is awesome. " + cool + " is cool. " +
 + alright + " is alright";
}

}
console.log(descriptions(undefined, "jack", "jefferson"));

这是工作代码。 您还可以传递一个空字符串。

Answer 4

在ECMAScript 6中，如果您更改参数以接收对象并利用分解分配的优势，则可以完成此操作。

 function descriptions({awesome: awesome = "no one", cool: cool = "", alright: alright = ""} = {}) { return awesome + " is awesome. " + cool + " is cool. " + alright + " is alright"; } var res = descriptions({ cool: "john", alright: "jane" }); document.body.textContent = res; 

因此，我们可以模拟命名参数。 大括号是呼叫者唯一需要的东西。

当然，对浏览器的支持是有限的，但是可以使用编译器。

Answer 5

您可以通过传递一个对象来做到这一点：

function descriptions(info) {
    // Avoid TypeError if no argument is passed
    if (!info) {
        info = {};
    }

    return (info.awesome || "no one") + " is awesome. " + (info.cool || "no one") + " is cool. " + (info.alright || "no one") + " is alright.";
}

// Use:
console.log(descriptions({
    awesome: "Strong Bad",
    cool: "The Cheat",
    alright: "Strong Sad"
}));

Answer 6

您可以使用其他方法：

var coolLevels = {
  isCool: ["Jack", "John"]
, isAlright: ["Jane", "Jefferson"]
, isAwesome: []
}

function describe(people, coolLevel, phrase) {
  return people.filter(function(person){
    return Boolean(coolLevel.indexOf(person))
  }).join(", ") + phrase
}

function descriptions(people){
  var awesome = describe(people, coolLevels.isAwesome, ' is awesome.')
  var cool = describe(people, coolLevels.isCool, ' is cool.')
  var alright = describe(people, coolLevels.isCool, ' is alright.')

  return awesome + cool + alright
}

演示： https : //jsbin.com/kahawuhelu/edit?js，控制台，输出

Answer 7

您可以传递undefined ， null或""作为第一个参数。 例如：

descriptions(null, "jack", "jefferson");

由于您已经使用了awesome || "no one" awesome || "no one" ，任何虚假的价值就足够了。

---

另一种方法是更改​​函数以接收对象：

function descriptions(options) {
  return (options.awesome || "no one") + " is awesome. " + options.cool + " is cool. " + 
    options.alright + " is alright";
}

descriptions({ cool: "jack", alright: "jefferson" });

---

现在，根据您的浏览器支持，您可以使用ES6解构参数：

const descriptions = ({ awesome = 'no one', cool, alright }) => (
  `${awesome} is awesome. ${cool} is cool. ${alright} is alright`
);

descriptions({ cool: 'jack', alright: 'jefferson' });