javascript string.split（'，'）在应创建数组时生成对象

Question

var _={};

_.bullets='1,2,3';

console.log(typeof bullets);

string

console.log(_.bullets);

var bullets=_.bullets.split(',');

console.log(bullets);    //REF 1

["1", "2", "3"]

console.log(typeof bullets);

object

Why is it not array? I can't figure out what I am doing wrong here

UPDATE

console.log([1,2,3]);
console.log(bullets);    //REF 1

[1, 2, 3]

["1", "2", "3"]

What is the difference (one is a string one is a number?)

Answer 1

typeof never returns 'array' . For instances of Array , it returns 'object' :

Table 20 — typeof Operator Results

• Undefined : "undefined"
• Null : "object"
• Boolean : "boolean"
• Number : "number"
• String : "string"
• Object (native and does not implement [[Call]]) : "object"
• Object (native or host and does implement [[Call]]) : "function"
• Object (host and does not implement [[Call]]) : Implementation-defined except may not be "undefined", "boolean", "number", or "string".

Source: ECMAScript spec

Answer 2

Use Array.isArray(a) or a instanceof Array .

Arrays are objects, so typeof returns object .

Answer 3

Technically typeof fits for primitive types while instanceof fits for reference types .

If you use typeof for some reference types ( Array, Object ), it will return "object" . Function is the third reference type ; it behaves differently ( typeof wise) as it will return "function" when typeof new Function() .

Based on your example you can deduce that string is a primitive type in JavaScript as typeof "blabla" === string (which returns true). Yes that's something curious if you come from a traditional strongly typed language such as Java or C#.

Answer 4

typeof returns 'object' when supplied array values. To test for an array you can do something like this (from JavaScript the Good Parts ):

var is_array = function (value) {
     return value &&
     typeof value === 'object' &&
     typeof value.length === 'number' &&
     typeof value.splice === 'function' &&
     !(value.propertyIsEnumerable('length'));
};