【JS】Determine that the object is empty

2021.03.06

There are several ways to determine that an object is empty (={}) in javaScript, so make a note of it.

目次

Object.keys(obj).length

Object.keys() - JavaScript | MDN
Object.keys() は静的メソッドで、指定されたオブジェクトが持つプロパティの名前の配列を、通常のループで取得するのと同じ順序で返します。
developer.mozilla.org

Here are some of the many things I’ve researched.

This is how to get and determine the Key array of Objects using Object.keys(obj).length.

function isEmpty(obj) {
  return ! Object.keys(obj).length
}

console.log(isEmpty({})) // -> true
console.log(isEmpty({'a': 'a'})) // -> false

You can use the same Object.keys(obj).length to judge even if it looks like this.

var obj = {}

console.log(0 === Object.keys(obj).length) // -> true
console.log(! Object.keys(obj).length) // -> true

for(… in…)

The above-mentioned method of using Object.keys().length seems to be extremely slow depending on the chrome version.

The current one seems to have already been fixed, but if you have to deal with an older version, you may need to consider using the following:

function isEmpty(obj) {
  for (let i in obj) {
    return false
  }
  return true
}

console.log(isEmpty({})) // -> true
console.log(isEmpty({'a': 'a'})) // -> false

As you can guess from here, you may see slowing down in other browsers (older versions of ).

JSON.stringify(obj)

JSON.stringify() - JavaScript | MDN
JSON.stringify() メソッドは、ある JavaScript のオブジェクトや値を JSON 文字列に変換します。置き換え関数を指定して値を置き換えたり、置き換え配列を指定して指定されたプロパティのみを含むようにしたりすることも...
developer.mozilla.org

I can’t do this, but it seems to be slow. The details are unknown because we have not measured it.

var obj = {}

console.log(JSON.stringify(obj) === '{}') // -> true

Summary

Basically, if you use the first Object.keys(obj).length, it seems to be no problem.
If you need to make this decision over and over again, you need to check the operating speed and choose what to use.

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