Cast javascript object to array. How to?_问答_开发者

Cast javascript object to array. How to?

开发者 https://www.devze.com 2023-01-18 16:18 出处：网络

I have made this sandbox test: <html> <head> <title>whatever</title> <script type=\"text/javascript\">

I have made this sandbox test:

<html>
    <head>
        <title>whatever</title>
        <script type="text/javascript">
            function myLittleTest() {
                var obj, arr, armap;

                arr = [1, 2, 3, 5, 7, 11];

                obj = {};
                obj = arr;
                alert (typeof arr);
                alert (typeof obj);

                // doesn't work in IE
                armap = obj.map(function (x) { return x * x; });
                alert (typeof armap);

            }
            myLittleTest();
 开发者_运维百科       </script>
    </head>
    <body>
    </body>
</html>

I realize I can use jQuery's function $.map for making that line of code work, but, what am I missing on javascript datatypes?

If you have an array-like object, (like arguments, for example,) you can get a real array made from it by calling Array.prototype.slice.call(o).

var o = {0:"a", 1:'b', length:2};
var a = Array.prototype.slice.call(o);

a will be ["a", "b"]. This will only work right if you have a correctly set length property.

I think you are trying too hard...

It's easiest with jQuery (or similar library)

For this object:

var obj = {a: 1, b: 2, c: 3};

Arrays have a fixed key system so for the object above, you've got to throw away either the keys (a, b, c) or the values (1, 2, 3)

So either this:

var arr = $.map(obj, function (value, key) { return value; });

or this:

var arr = $.map(obj, function (value, key) { return key; });

A year ago now, but I may as well mention jQuery's makeArray function http://api.jquery.com/jQuery.makeArray/

I'm pretty sure this isn't a type problem, it's because IE didn't have the Array.map() function until IE 9. See http://msdn.microsoft.com/en-us/library/k4h76zbx(v=VS.85).aspx for a list of supported functions. See http://msdn.microsoft.com/en-us/library/ff679976(v=VS.94).aspx for a description of the Array.map() function in IE 9.

Use a for loop for max browser compatibility.

In Javascript all arrays are objects, but not all object are arrays. Take a look at this Perfection Kills page which describes how to check that something is an Array.

To check for an array, you can use Object.prototype.toString.call(theObject). This will return [object Array] for an object that is an Array and [object Object] for an object that's not an Array (see example below):

            function myLittleTest() 
            {
                var obj, arr, armap, i;    

                  // arr is an object and an array
                arr = [1, 2, 3, 5, 7, 11]; 

                obj = {}; // obj is only an object... not an array

                alert (Object.prototype.toString.call(obj));
                  // ^ Output: [object Object]

                obj = arr; // obj is now an array and an object

                alert (Object.prototype.toString.call(arr));
                alert (Object.prototype.toString.call(obj));
                  // ^ Output for both: [object Array]

                // works in IE
                armap = [];
                for(i = 0; i < obj.length; ++i)
                {
                    armap.push(obj[i] * obj[i]);
                }

                alert (armap.join(", ")); 

            }
            // Changed from prueba();
            myLittleTest();

jsFiddle example

Among many other small utilities for manipulating objects and arrays, Underscore.js offers a toArray(obj) helper method. Documentation here: http://underscorejs.org/#toArray

It's not totally obvious from the way the documentation is written, but it works like a charm on arbitrary objects. When given an object, it iterates over the values and returns a list that contains just those values.