JavaScript 原型和修改原始对象

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英文:

Javascript prototype and modify original object

问题

You can update the original object by modifying the prototype method to reverse the array in place. Here's the modified code:

Array.prototype.myReverse = function() {
  let length = this.length;
  for (let i = 0; i < Math.floor(length / 2); i++) {
    let temp = this[i];
    this[i] = this[length - 1 - i];
    this[length - 1 - i] = temp;
  }
  return this;
}

let a = [9, 0, 3, 4];
console.log("Before ", a); // [9, 0, 3, 4]
console.log("reverse - ", a.myReverse()); // [4, 3, 0, 9]
console.log("After ", a); // [4, 3, 0, 9]

This updated myReverse function reverses the original array in place, modifying the original object.

英文:

How can we update passed object in prototype? I have created similar prototype as Array.reverse, but how I can modify original object?

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

Array.prototype.myReverse = function() {
  let arr = [];
  for (let i = 0; i &lt; this.length; i++) {
    arr.unshift(this[i]);
  }
  return arr;
}

let a = [9, 0, 3, 4];
console.log(&quot;Before &quot;, a); // [9, 0, 3, 4]
console.log(&quot;reverse - &quot;, a.myReverse()); // [4, 3, 0, 9]
//not modifying original object , how to modify original object
console.log(&quot;After &quot;, a); // [9, 0, 3, 4]

<!-- end snippet -->

I have check few examples but I didnt get how to update orginal object inside prototype
How can we crate a prototype which will update original object (Careful: reverse is destructive -- it changes the original array.) If not possible for predefined Array then how we can create similar MyArray to write a prototype for updating original object.

答案1

得分: 2

你不能直接赋值给 this,但你仍然可以更改其属性。因此,保持你发布的代码风格,你可以按照以下方式进行操作:

Array.prototype.myReverse = function() {
  let arr = [...this]
  for (let i = 0; i < this.length; i++) {
    this[i] = arr.pop()
  }
}
英文:

You cannot assign this directly, but you can still change its properties. So keeping in the style of the code you posted, you could do something along the lines of:

Array.prototype.myReverse = function() {
  let arr = [...this]
  for (let i = 0; i &lt; this.length; i++) {
    this[i] = arr.pop()
  }
}

答案2

得分: 0

如果你想原地反转数组(并且如果你愿意,返回它),你可以创建一个临时栈,通过弹出数组的头部直到它为空,然后将临时元素推入,就好像它们是在队列中一样。

  1. 临时栈:
  • ARR→POP ⇒ TMP→PUSH(LILO)
  • ARR→SHIFT ⇒ TMP→UNSHIFT(FIFO)
  1. 从临时栈中:
  • TMP→POP ⇒ ARR→UNSHIFT(LOFI)
  • TMP→SHIFT ⇒ ARR→PUSH(FOLI)

其中 ARR 是自引用数组。

英文:

If you want to reverse the array in-place (and return it if you would like), you can create a temporary stack by popping the head of the array until it is empty and then pushing the temporary elements as if they were in a queue.

  1. To temp:
  • ARR→POP ⇒ TMP→PUSH (LILO)
  • ARR→SHIFT ⇒ TMP→UNSHIFT (FIFO)
  1. From temp:
  • TMP→POP ⇒ ARR→UNSHIFT (LOFI)
  • TMP→SHIFT ⇒ ARR→PUSH (FOLI)

Where ARR is the self-reference array.

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

if (Array.prototype.reverseItems === undefined) {
  Array.prototype.reverseItems = function() {
    let tmp = []
    while (this.length &gt; 0) tmp.push(this.pop())    // or `tmp.unshift(this.shift()`
    while (tmp.length  &gt; 0) this.unshift(tmp.pop()) // or `this.push(tmp.shift())`
    return this
  }
}

let original = [ 9, 0, 3, 4 ]
original.reverseItems() // in-place
console.log(&#39;Reversed:&#39;, original.join(&#39;,&#39;))

<!-- end snippet -->

答案3

得分: -1

@pointy 感谢建议..

我已经修改了这个对象的属性并更新了原始对象

Array.prototype.myReverse = function () {
  let arr = this.slice(); // 创建数组的副本
  this.splice(0, this.length); // 从数组中删除所有元素
  for (let i = 0; i < arr.length; i++) {
    this.unshift(arr[i]);
  }
  return this;
}

let a = [9, 0, 3, 4];

console.log("Before ", a);
console.log("reverse - ", a.myReverse());
console.log("After ", a);

其他用于模拟现有数组原型的链接

https://medium.com/@ofirrifo/naive-implementation-of-js-array-methods-a56319cad6b8

https://gist.github.com/alexhawkins/28aaf610a3e76d8b8264

https://stackoverflow.com/questions/44736780/node-js-change-number-object-value-inside-prototype

英文:

@pointy Thanks for suggestion..

I have modified properties of this and updated original object

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

Array.prototype.myReverse = function () {
 let arr = this.slice(); // creating a copy of array
  this.splice(0,this.length); // removing all elements from array
  for(let i = 0; i&lt;arr.length;i++){
    this.unshift(arr[i]);
  }
  return this;
}

let a = [9,0,3,4];

console.log(&quot;Before &quot;,a);
console.log(&quot;reverse - &quot;, a.myReverse());
console.log(&quot;After &quot;, a);

<!-- end snippet -->

Few other links for native imlimatation of exsiting array prototypes

https://medium.com/@ofirrifo/naive-implementation-of-js-array-methods-a56319cad6b8

https://gist.github.com/alexhawkins/28aaf610a3e76d8b8264

https://stackoverflow.com/questions/44736780/node-js-change-number-object-value-inside-prototype

huangapple
  • 本文由 发表于 2020年1月6日 21:53:24
  • 转载请务必保留本文链接:https://go.coder-hub.com/59613346.html
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