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1

In JavaScript, there are objects that pretend to be arrays (or are "array-like"). Such objects are arguments, NodeLists (returned from getElementsByClassName, etc.), and jQuery objects.

When console.logged, they appear as arrays, but they are not. I know that in order to be array-like, an object must have a length property.

So I made an "object" like this:

function foo(){
    this.length = 1;
    this[0] = "bar";
}

var test = new foo;

When I console log(test), I get (as expected) a foo object. I can "convert" it to an array using

Array.prototype.slice.call(test)

But, I don't want to convert it, I want it to be array-like. How do I make an array-like object, so that when it's console.logged, it appears as an array?

I tried setting foo.prototype = Array.prototype, but console.log(new foo) still shows a foo object, and not an array.

share|improve this question
2  
"How do I make an array-like object, so that when it's console.logged, it appears as an array?" Just because a console isn't displaying it using Array literal syntax, or some other syntax that makes you think of an Array, doesn't mean it isn't "array-like". How a console displays your data has no bearing on what that data is. –  squint Aug 9 '12 at 15:31
1  
@amnotiam, while that is true, it's a case where I've found it useful to assist the console in assisting me. When I log an "array-like" object, I don't really care that much about the object as much as its contents. –  zzzzBov Aug 9 '12 at 15:33
    
@amnotiam: I was just kinda curious how jQuery objects and arguments worked. I wanted to know why they are logged as arrays. :-P –  Rocket Hazmat Aug 9 '12 at 15:38
    
@zzzzBov: I don't disagree with that. I'm just saying there's a distinction between having an "array-like object", and how some console displays that object. –  squint Aug 9 '12 at 15:38
1  
@Rocket: I understand that. But it's not how jQuery objects or arguments works. It's how various consoles work, which may be different from each other. Perhaps I misinterpreted your sentence above a bit. –  squint Aug 9 '12 at 15:39
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3 Answers

up vote 13 down vote accepted

Depends specifically on the console. For custom objects in Chrome's developer console, and Firebug you'll need both the length and splice properties. splice will also have to be a function.

a = {
    length: 0,
    splice: function () {}
}
console.log(a); //[]
share|improve this answer
    
Neat! Adding the splice property did show it as an array! –  Rocket Hazmat Aug 9 '12 at 15:21
    
@Rocket, it's why jQuery objects look like arrays in the console, even though they don't inherit from Array. –  zzzzBov Aug 9 '12 at 15:21
    
Then how is arguments.splice set to undefined? –  Rocket Hazmat Aug 9 '12 at 15:21
2  
Anyway, its just an illusion of console implementations. Afterall, there is no Array in ECMAscript (when we forget about TypedArrays). –  jAndy Aug 9 '12 at 15:22
    
@Rocket, type checking for specific types was used in Firebug. I don't know what chrome uses. For custom consoles, you could check for Object.prototype.toString.call(obj) === '[object Arguments]' in some browsers. –  zzzzBov Aug 9 '12 at 15:26
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up vote 2 down vote

Is this any use: extended array prototype, seems like he's doing what you did and creating the prototype as an array, but including an extra method (that may or may not work, I've not tested this):

var MyArray = function() {
};

MyArray.prototype = new Array;

MyArray.prototype.forEach = function(action) {
    for (var i = 0, l=this.length; i < l, ++i) {
        action(this[i]);
    }
};

Hope it helps in some way.

share|improve this answer
    
That adds all the functions from Array.prototype to MyArray, but with arguments and jQuery objects, they don't have those. –  Rocket Hazmat Aug 9 '12 at 15:23
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up vote 0 down vote

I think this is what you are looking for. Override the toString function.

foo.prototype.toString = function()
{
    return "[object Foo <" + this[0] +">]";
}
share|improve this answer
    
Not quite. What I want is when you console.log it, it displays like an array []. In Chrome, when you console.log(arguments) it's looks like an array, but it's really not. –  Rocket Hazmat Aug 9 '12 at 15:29
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