Javascript Array.prototype.map（）函数与JS对象的行为

我正在尝试以下代码：

 let obj ={};
    let newIngredients = ["Hello", "Distraction", "Nothing", "Love"].map(el => {
        obj.count= Math.random()*el.length;
        obj.ingredient= el;
        return obj;
    });
    console.log(newIngredients);

这是我得到的输出：

(4) [{…}, {…}, {…}, {…}]
0: {count: 1.4648989727265578, ingredient: "Love"}
1: {count: 1.4648989727265578, ingredient: "Love"}
2: {count: 1.4648989727265578, ingredient: "Love"}
3: {count: 1.4648989727265578, ingredient: "Love"}
length: 4
__proto__: Array(0)

这不是我想要的。但当我输入以下内容时

let obj;
let newIngredients = ["Hello", "Distraction", "Nothing", "Love"].map(el => {
      obj = {
               count: Math.random()*el.length,
               ingredient: el
            } ;
      return obj;
 });
 console.log(newIngredients);

它返回我实际需要的以下输出：

(4) [{…}, {…}, {…}, {…}]
0: {count: 4.2813861024052615, ingredient: "Hello"}
1: {count: 5.850654082147917, ingredient: "Distraction"}
2: {count: 6.646446034466489, ingredient: "Nothing"}
3: {count: 1.7062874250924214, ingredient: "Love"}
length: 4
__proto__: Array(0)

---

有人能解释一下为什么这两个代码段的行为会有差异吗？

在第一个示例中，您只创建了一个对象，然后将其放入数组中四次：

let obj ={}; // <===== Creates the one object
let newIngredients = ["Hello", "Distraction", "Nothing", "Love"].map(el => {
    obj.count= Math.random()*el.length;
    obj.ingredient= el;
    return obj; // <===== Puts it in the array four times
});
console.log(newIngredients);

就像这样做：

let first={}；
第一，a=1；
让第二个=第一个；
第二，a=2；
console.log（first.a）；//这与Array.prototype.map（）无关，而是与javascript中的对象行为有关

例如，如果您运行此


让obj={}；
设prev=obj；
let NewComponents=[“你好”，“分心”，“没事”，“爱”]。地图（el=>{
obj={
计数：Math.random（）*el.length，
成分：香精
};
如果（obj==上一个）{
console.log（true）；
}否则{
console.log（false）
}
prev=obj；
返回obj；
});
console.log（新成分）
+−−−−−−−−−−−−−−−−−−−−−−−−−−−+
obj:Ref11654−−−−−−−−−−−−−−−−−−−−−−−+−+−+−+−>|         (object)          |
                                  / / / /   +−−−−−−−−−−−−−−−−−−−−−−−−−−−+
                                  | | | |   | count: 1.4648989727265578 |
                                  | | | |   | ingredient: "Love"        |
                                  | | | |   +−−−−−−−−−−−−−−−−−−−−−−−−−−−+
                                  | | | |
                  +−−−−−−−−−−−−−+ | | | |
newIngredients−−−>|   (array)   | | | | |
                  +−−−−−−−−−−−−−+ | | | |
                  | 0: Ref11654 |−+ | | |
                  | 1: Ref11654 |−−−+ | |
                  | 2: Ref11654 |−−−−−+ |
                  | 3: Ref11654 |−−−−−−−+
                  +−−−−−−−−−−−−−+