I have an javascript object of arrays like,
var coordinates = { "a": [ [1, 2], [8, 9], [3, 5], [6, 1] ], "b": [ [5, 8], [2, 4], [6, 8], [1, 9] ] }; but coordinates.length returns undefined. Fiddle is here.
- 2An object doesn't have any length, arrays doesGuillaume Munsch– Guillaume Munsch2015-06-16 07:47:02 +00:00Commented Jun 16, 2015 at 7:47
- What length did you expect? 2? 8? 16?Bergi– Bergi2015-06-16 07:50:53 +00:00Commented Jun 16, 2015 at 7:50
- I found this question while investigating why in my case an actual array assigned to [] and then having one item pushed to it, has a length of undefined.Victor Zakharov– Victor Zakharov2023-11-09 12:24:49 +00:00Commented Nov 9, 2023 at 12:24
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3 Answers
That's because coordinates is Object not Array, use for..in
var coordinates = { "a": [ [1, 2], [8, 9], [3, 5], [6, 1] ], "b": [ [5, 8], [2, 4], [6, 8], [1, 9] ] }; for (var i in coordinates) { console.log(coordinates[i]) } or Object.keys
var coordinates = { "a": [ [1, 2], [8, 9], [3, 5], [6, 1] ], "b": [ [5, 8], [2, 4], [6, 8], [1, 9] ] }; var keys = Object.keys(coordinates); for (var i = 0, len = keys.length; i < len; i++) { console.log(coordinates[keys[i]]); } 
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coordinates is an object. Objects in javascript do not, by default, have a length property. Some objects have a length property:
"a string - length is the number of characters".length ['an array', 'length is the number of elements'].length (function(a, b) { "a function - length is the number of parameters" }).length You are probably trying to find the number of keys in your object, which can be done via Object.keys():
var keyCount = Object.keys(coordinates).length; Be careful, as a length property can be added to any object:
var confusingObject = { length: 100 }; 
1 Comment
frogatto
I didn't know
(function(){}).length is number of arguments. Thanks for your sharing.http://jsfiddle.net/3wzb7jen/2/
alert(Object.keys(coordinates).length); 