在JavaScript中循环访问数组 [英] Loop through an array in JavaScript

问题描述

在Java中，您可以使用来循环循环中的对象，如下所示：

  String [] myStringArray = {Hello，World}; 
 for（String s：myStringArray）
 {
 //做某事
} 
  

你可以在JavaScript中做同样的事情吗？

解决方案

对于循环：

  var myStringArray = [Hello，World]; 
 var arrayLength = myStringArray.length; 
 for（var i = 0; i< arrayLength; i ++）{
 alert（myStringArray [i]）; 
 //做点什么
} 
  

@zipcodeman建议使用 for ... in 语句，但是为了迭代数组 for-in 应该被避免，那么这个语句的意思是枚举对象属性。

它不应该用于类似数组的对象，因为：

• 不保证迭代顺序，数组顺序不能按数字顺序访问。


• 继承的属性也被枚举。 b
  $ b $ p
  $ b

  第二点是它可以给你很多问题，例如，如果扩展 Array.prototype


















pre> Array.prototype.foo =foo！;
var array = ['a'，'b'，'c'];

（var i在数组中）{
alert（array [i]）;







  上面的代码会提示a，b，c 和foo！。



  如果使用一些依赖本机原型增强的库（例如MooTools），那么这尤其是个问题。

  
  
  

  如前所述， for-in 语句用于枚举对象属性，例如：
  
  

    var obj = {
  a：1，
  b：2，
  c：3 
  }; 
   
  （obj）{
   if（obj.hasOwnProperty（prop））{
   // if（Object.prototype.hasOwnProperty.call（obj，prop ））... 
   alert（prop：+ prop +value：+ obj [prop]）
  } 
  } 
    

  在上面的例子中， hasOwnProperty 方法只允许枚举自己的属性，就是这样，只有对象的物理属性，没有继承属性。

  
  
  

  我建议你阅读下面的文章：

  
  
  
  
  
  • Enumeration VS Iteration
    
  
  

  In Java you can use a for loop to traverse objects in an array as follows:

  String[] myStringArray = {"Hello", "World"};
  for (String s : myStringArray)
  {
      // Do something
  }
  

  Can you do the same in JavaScript?

  解决方案

  Use a sequential for loop:

  var myStringArray = ["Hello","World"];
  var arrayLength = myStringArray.length;
  for (var i = 0; i < arrayLength; i++) {
      alert(myStringArray[i]);
      //Do something
  }
  

  @zipcodeman suggests the use of the for...in statement, but for iterating arrays for-in should be avoided, that statement is meant to enumerate object properties.

  It shouldn't be used for array-like objects because:

  • The order of iteration is not guaranteed, the array indexes may not be visited in numeric order.
  • Inherited properties are also enumerated.

  The second point is that it can give you a lot of problems, for example, if you extend the Array.prototype object to include a method there, that property will be also enumerated.

  For example:

  Array.prototype.foo = "foo!";
  var array = ['a', 'b', 'c'];
  
  for (var i in array) {
    alert(array[i]);
  }
  

  The above code will alert, "a", "b", "c" and "foo!".

  That be particularly a problem if you use some library that relies heavily on native prototypes augmention (such as MooTools for example).

  The for-in statement as I said before is there to enumerate object properties, for example:

  var obj = {
    "a": 1,
    "b": 2,
    "c": 3
  };
  
  for (var prop in obj) {
    if (obj.hasOwnProperty(prop)) { 
    // or if (Object.prototype.hasOwnProperty.call(obj,prop)) for safety...
      alert("prop: " + prop + " value: " + obj[prop])
    }
  }
  

  In the above example the hasOwnProperty method allows you to enumerate only own properties, that's it, only the properties that the object physically has, no inherited properties.

  I would recommend you to read the following article:

  • Enumeration VS Iteration

  这篇关于在JavaScript中循环访问数组的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！