Say I have a function like so:
function foo(bar) {
if (bar > 1) {
return [1,2,3];
} else {
return 1;
}
}
And say I call foo(1), how do I know it returns an array or not?
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3You're making your life harder than it needs to be. I would consider it better style if the function always returns an array.Miles– Miles2009-07-30 19:01:41 +00:00Commented Jul 30, 2009 at 19:01
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5 Answers
I use this function:
function isArray(obj) {
return Object.prototype.toString.call(obj) === '[object Array]';
}
Is the way that jQuery.isArray is implemented.
Check this article:
answered Jul 29, 2009 at 20:34
Christian C. Salvadó
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2 Comments
Artilheiro
Perfect! I am using jQuery so I'll just use that. The article helped too.
shabunc
in modern browsers we have Array.isArray function, so better write smth like if !Array.isArray { ... here goes the definition ...}
if(foo(1) instanceof Array)
// You have an Array
else
// You don't
Update: I have to respond to the comments made below, because people are still claiming that this won't work without trying it for themselves...
For some other objects this technique does not work (e.g. "" instanceof String == false), but this works for Array. I tested it in IE6, IE8, FF, Chrome and Safari. Try it and see for yourself before commenting below.
12 Comments
Boldewyn
That will only work, if you declare an array via
new Array(), not with the [] shorthand. See the section 'Description' under the above URL.
James
And this won't work for different global contexts; like an object from within an iframe...
Prestaul
@Boldewyn, that is not true. It is true for some other objects (e.g. "" instanceof String == false), but this works for Array. Try it and see for yourself.
Prestaul
@Josh Stodola, so can Object.prototype.toString. You can overwrite nearly everything in js, but there are some assumptions you have to make in order to answer a question.
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Here is one very reliable way, take from Javascript: the good parts, published by O'Reilly:
if (my_value && typeof my_value === 'object' && typeof my_value.length === 'number' &&
!(my_value.propertyIsEnumerable('length')) { // my_value is truly an array! }
I would suggest wrapping it in your own function:
function isarray(my_value) {
if (my_value && typeof my_value === 'object' && typeof my_value.length === 'number' &&
!(my_value.propertyIsEnumerable('length'))
{ return true; }
else { return false; }
}
answered Jul 30, 2009 at 18:05
Gordon Gustafson
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1 Comment
Jacob Relkin
You could just
return the result of the expression instead of an if..else. :PTo make your solution more general, you may not care whether it is actually an Array object. For example, document.getElementsByName() returns an object that "acts like" an array. "Array compliance" can be assumed if the object has a "length" property.
function is_array_compliant(obj){
return obj && typeof obj.length != 'undefined';
}
