Javascript: How to check my variable is empty or not using JavaScript Type Conversion?

Question

I tried to initialize an empty array in JavaScript but it return something in it. then I tried with typescript it allow to initialize empty array. but I want it in JavaScript so how can I do?

Can anyone help?

Thanks in advance.

javascript code:

var emptyArr = [];
var emptyString = "";
var emptyNumber;
var numberWithZeroValue = 0;
var emptyBoolean = false;
console.log("emptyArr: " + !!emptyArr);
console.log("emptyString: " + !!emptyString);
console.log("emptyNumber: " + !!emptyNumber);
console.log("numberWithZeroValue: " + !!numberWithZeroValue);
console.log("emptyBoolean: " + !!emptyBoolean);

output:

emptyArr: true        //it returning somthing in it.
emptyString: false
emptyNumber: false
numberWithZeroValue: false
emptyBoolean: false

javascript does't allow to declare type of variable so I tried with typescript.

typescript code:

var emptyArr: Array;
var emptyString: String = "";
var emptyNumber: Number;
var numberWithZeroValue: Number = 0;
var emptyBoolean: Boolean = false;

console.log("emptyArr: " + !!emptyArr);
console.log("emptyString: " + !!emptyString);
console.log("emptyNumber: " + !!emptyNumber);
console.log("numberWithZeroValue: " + !!numberWithZeroValue);
console.log("emptyBoolean: " + !!emptyBoolean);

output:

emptyArr: false     //it returning empty array.
emptyString: false
emptyNumber: false
numberWithZeroValue: false
emptyBoolean: false

Note: typescript return an array is empty but javascript return something in it.

Update: I don't want to check with array.length because my variable is any of type like String, Number, Array, Boolean, etc. I want to check it like return !!myVariable

You need to learn the syntax of both languages. Start with JavaScript. — Aluan Haddad, Mar 31 '18 at 10:50
it's a problem of definition. What is considered an empty array and _how to check if it's empty_. — Jeff, Mar 31 '18 at 10:52
https://stackoverflow.com/questions/11743392/check-if-array-is-empty-or-exists — Jeff, Mar 31 '18 at 10:53
Possible duplicate of [Check if array is empty or exists](https://stackoverflow.com/questions/11743392/check-if-array-is-empty-or-exists) — Aliaksandr Sushkevich, Mar 31 '18 at 10:57

connexo · Answer 1 · 2018-03-31T10:59:29.983

You did create an empty Array, no problems with your creation code.

An Array in Javascript is considered empty if it holds no elements.

You check for an empty array in Javascript like this:

console.log("emptyArr: " + !!emptyArr.length);

let emptyArr = []; // or new Array();
console.log("emptyArr: " + !!emptyArr.length);
if (emptyArr.length) {
  console.log("Array is not empty");
} else {
  console.log("Array is empty");
}

Since the following values evaluate to false in a Boolean expression in Javascript

0, "", undefined, null, false

instead of if (!!emptyArr.length) you simply go if (emptyArr.length) in Javascript. These values (except false) are called falsy in Javascript.

Abslen Char · Answer 2 · 2018-03-31T10:57:38.510

1

This the proper way to check for an empty array in javascript

var emptyArr = [];
var emptyString = "";
var emptyNumber;
var numberWithZeroValue = 0;
var emptyBoolean = false;
if(emptyArr.length == 0){
console.log(" its an emptyArr");
}

console.log("emptyString: " + !!emptyString);
console.log("emptyNumber: " + !!emptyNumber);
console.log("numberWithZeroValue: " + !!numberWithZeroValue);
console.log("emptyBoolean: " + !!emptyBoolean);

edited Mar 31 '18 at 10:57

answered Mar 31 '18 at 10:55

Abslen Char

3,071
3
15
29

In real life, you'd do `if(emptyArr.length)`. – connexo Mar 31 '18 at 10:56
@connexo i know , i didnt want to do it because it seems that the OP is not familiar with javascript yet – Abslen Char Mar 31 '18 at 10:56

score 0 · Answer 3 · answered Mar 31 '18 at 10:56

0

you can declare array in typescript like this.

var alphas:any[];

answered Mar 31 '18 at 10:56

Sunil

138
2
15

I want it in javascript – Vipul Solanki Mar 31 '18 at 10:59

score 0 · Answer 4 · answered Mar 31 '18 at 10:58

Maybe you want to know why vanillaJS array initialization equals true and typescript false.

This is because of the typescript transpiler. It transpiles var emptyArr: Array; into var emptyArr; and now you've the same result as your third vanillaJS line (var emptyNumber;).

Javascript: How to check my variable is empty or not using JavaScript Type Conversion?

4 Answers4