kazoottt-blog/src/content/post/how to check if a key is in the Object.md

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title	date	author	type	status	tags	finished	published	category	slug	description	NotionID-notionnext	link-notionnext	rinId
how to check if a key is in the Object	2024-05-06	KazooTTT	Post	Published	javascript Object	true	true	随手记	how-to-check-if-a-key-is-in-the-object	This document explains two methods to check if a property exists in a JavaScript object: the `in` operator and the `hasOwnProperty` method. The `in` operator returns `true` if the specified property is in the object or its prototype chain, and it requires the property name to be a string. The `hasOwnProperty` method also checks for property existence, specifically within the object itself, not its prototype chain, and it also requires the property key to be a string. Both methods are demonstrated with examples.	196ff681-16d8-47f1-a3d1-15a87b02aa5f	https://kazoottt.notion.site/how-to-check-if-a-key-is-in-the-Object-196ff68116d847f1a3d115a87b02aa5f	47

How to Check if a Key is in the Object

there are many methods.

in Operator

in - JavaScript | MDN

The in operator returns true if the specified property is in the specified object or its prototype chain.

how to use?

for example:

const dict = { a: "a", b: "b" }
console.log("a" in dict)

attention: the attribute name should be string.

that is to say:

• a in dict ❎
• "a" in dict ✅

Object API: hasOwnProperty

Object.prototype.hasOwnProperty() - JavaScript | MDN

The complete expression is Object.prototype.hasOwnProperty().

how to use it ?

const dict = {
  a: "a",
  b: "b",
}
console.log(dict.hasOwnProperty("a"))

the same is the attribute key should be a string.

• a in dict ❎
• "a" in dict ✅