Association array analysis in JavaScript

Normally, the array is implicitly filled or the specified array subscript is displayed. However, arrays in JS can assign values to elements in the form of names, which forms an associated array, for example:

Copy codeThe Code is as follows:
Var arr = new Array ();
Arr ["china"] = "beijing, niaoling, hulan ";
Arr ["usa"] = "newyork, washington, atlanta ";
Arr ["japan"] = "tokyo ";

Alert (arr ["china"]);
Alert (arr ["japan"]);

Alert (arr [0]);

Note that the preceding alert (arr [0]); returns undifined. This means that, in an associated array, you cannot access the array elements in the traditional subscript method, but you must use the element name.
This method of accessing array elements by name has the advantages of high readability, flexibility and convenience. To some extent, it can be used as a hash table in JS.
The for in loop is required to traverse the correlated array. Note the following two different traversal methods in the Code:

Copy codeThe Code is as follows:
Var arr = new Array ();
Arr ["china"] = "beijing, niaoling, hulan ";
Arr ["usa"] = "newyork, washington, atlanta ";
Arr ["japan"] = "tokyo ";

// This method can traverse the names in the joined Array
For (var item in arr ){
Alert (item );
}

// This method can traverse the elements in the joined array.
For (var item in arr ){
Alert (arr [item]);
}