Either we check type of array or object it always print object in JavaScript. Why so?
let arr=[1,3,4];
let obj={1:"44",num:44};
console.log(typeof(arr)) //object
console.log(typeof(obj)) //object
Is there any way to see typeof(array) as array?
3 Answers
Try using the instanceof operator
const arr = [];
console.log(arr instanceof Array); // true
const obj = {};
console.log(obj instanceof Array); // false
Comments
Because an array is technically a type of object - just with certain abilities and behaviors, for instance additional methods like Array.prototype.push() and Array.prototype.unshift(). Arrays are regular objects where there is a particular relationship between integer-key-ed properties and the length property.
To determine whether you have an array specifically, you can use Array.isArray().
1 Comment
user2864740
The language/specification could have been written to support it.. and alas, it was not and here we are. The rationalization of an array “being an object” being the crucial designator here is tenuous: after all, a function is an actual Object type (not a primitive), yet it is a “function” in relation to the typeof operator. So the reason is due to an arbitrary design decision stemming from the very inception versions. - See codeburst.io/… and the specification.
In JavaScript, almost everything is an Object.
It uses prototype chain to achieve inheritance.
you can just console.log( [] ) and see the prototype part to see that it inherit from objects.
Here is a simple way to make an your own Array.
function MyArray(){
Object.defineProperty(this, 'length', {
value: 0,
enumerable: false,
writable: true,
})
}
MyArray.prototype.push = function(elem){
this[this.length] = elem
this.length++
return this.length
}
MyArray.prototype.isMyArray = function(instance){
return instance instanceof MyArray
}
var arr = new MyArray()
arr.push(1)
arr.push(2)
arr.push(3)
console.log('instance', MyArray.prototype.isMyArray( arr ))
// instance true
console.log('object', typeof arr)
// object object
9 Comments
user2864740
The assertion is incorrect: ‘everything’ (much less every value) is not an object in JavaScript. As a trivial example, “hello” is a primitive value of type string. It can be implicitly promoted to an object of type String. This distinction is important to not “wash away” as it applies to many ECMAScript rules, including === etc. Search for “ECMAScript Specification”.
albseb
Ok I meant to say almost. Of course there are primitives.
albseb
Also there are object wrappers
user2864740
Then ‘everything’ is incorrect.
albseb
var str = new String('string')
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Array.isArrayinstead to check whether something is an array.typeof(val)=="object" && !Array.isArray(val).instanceofortypeofor whatever, ask yourself: Do you really care? How 'bout looking to see if the object seems to have the things on it you need (feature detection) rather than worrying about what it is? This is usually called "duck typing," from the phrase "If it walks like a duck and talks like a duck..."' - Quote from the blog post Nifty Snippets: Say what? by @T.J.Crowder