Home / Questions / 266485
Accepted
David DPG
Asked: 2020-05-25 02:14:45 +0800 CST 2020-05-25 02:14:45 +0800 CST

What is the difference between initializing an object to null or initializing it to empty?

  • 772

My understanding is that when you want to create a new object in Javascript, it's best to use JSON notation:

let foo1 = {};
let foo2 = {};

foo1 = `Hola ${user}`;
foo2.name = user;

So I have been surprised when, when reviewing code that has been bequeathed to me, I have found something like:

let httpResponse = null;

if (condition) {
    httpResponse = 'Error processing request'
} else {
    httpResponse = JSON.parse(data)
}

Why have my peers put null to initialize the object? Are there differences between both ways?

javascript

1 Answers

  1. Best Answer

    I go by parts:

    let foo1 = {};
let foo2 = {};

foo1 = `Hola ${user}`;
foo2.name = user;

    This code is wrong . It works, but it does things that are not necessary:

    const user='Tú';
let foo1 = {};
let foo2 = {};

console.log(typeof foo1);
foo1 = `Hola ${user}`;
console.log(typeof foo1);

foo2.name = user;
console.log(foo2);

    As you can see, you first assign an empty object to foo1, but then you assign a string, so the initial object is lost. In the case of foo2 it makes sense because you are adding properties to the already created object.

    The same goes for this other code:

    let httpResponse = null; // es null

if (condition) {
    httpResponse = 'Error processing request' //es un string
} else {
    httpResponse = JSON.parse(data) // es un objeto
}

    Setting it to null is unnecessary because you have a if-else. If you had a if-else-if, there would be a chance that nothing would be assigned

    Finally, let's assume that your code really is more complex than what you have put in the example and it needs a default value. Initializing to nullmay make sense if your checks are strict, but remember that it null == undefinedis always true. In fact, as long as you're not working with numbers, it's more comfortable to do something like

    if (variable) {
   ...
}

    where variableit is considered false if it is null, undefined or an empty string. An object (empty or not), including an array (empty or not) or a string with length greater than 0 is considered true . With numbers, 0 is false and any other value, positive or not, is true.

    So what is the difference between having an empty object and having null/undefined? Well, what we have seen with foo2, you can add the properties you need to an empty object, while you cannot add the properties to a null/indefined object, since it would cause the well-known Cannot set property ... of null error :

    let vacio={};
let nulo = null;

vacio.a='hola';

try {
  nulo.a='hola';
} catch (e) {
  console.log('Algo falla:',e.toString());
}

    • 3