Object.length 在 JavaScript 中未定义
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Object.length undefined in javascript
提问by mpsbhat
I have an javascript object of arrays like,
我有一个数组的javascript对象，例如，
var coordinates = {
"a": [
[1, 2],
[8, 9],
[3, 5],
[6, 1]
],
"b": [
[5, 8],
[2, 4],
[6, 8],
[1, 9]
]
};
but coordinates.lengthreturns undefined.
Fiddle is here.
但coordinates.length返回未定义。
小提琴在这里。
采纳答案by Alexander T.
That's because coordinatesis Objectnot Array, use for..in
这是因为，coordinates是Object不是Array，使用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
或者 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]]);
}
回答by Armand
coordinatesis an object. Objects in javascript do not, by default, have a lengthproperty. Some objects have a length property:
coordinates是一个对象。默认情况下，javascript 中的对象没有length属性。一些对象具有长度属性：
"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 keysin your object, which can be done via Object.keys():
您可能正在尝试查找keys对象中的数量，这可以通过Object.keys()以下方式完成：
var keyCount = Object.keys(coordinates).length;
Be careful, as a lengthproperty can be added to any object:
小心，因为length属性可以添加到任何对象：
var confusingObject = { length: 100 };
回答by AshBringer
http://jsfiddle.net/3wzb7jen/2/
http://jsfiddle.net/3wzb7jen/2/
alert(Object.keys(coordinates).length);
