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I am trying to extract all the properties and methods from an object which happens to be a string: var str = "Hello World!"

If I use the mand Object.getOwnPropertyNames(str) I get a list of properties and methods: ["0", "1", "2", "3", "length"]. However I know there are other methods like .toUpperCase() which belong to the string object but they are not listed.

My question: why is the method .toUpperCase() not listed? What can I do to list it out with many others (.indexOf()...)?

Here is the code:

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>Display properties and methods from objects</title>
</head>
<body>
    <script type="text/javascript">
    var str= 'Hello World!'
    var listPropertiesMethods = Object.getOwnPropertyNames(str)
    console.log(listPropertiesMethods);
    </script>
</body>
</html>

I am trying to extract all the properties and methods from an object which happens to be a string: var str = "Hello World!"

If I use the mand Object.getOwnPropertyNames(str) I get a list of properties and methods: ["0", "1", "2", "3", "length"]. However I know there are other methods like .toUpperCase() which belong to the string object but they are not listed.

My question: why is the method .toUpperCase() not listed? What can I do to list it out with many others (.indexOf()...)?

Here is the code:

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>Display properties and methods from objects</title>
</head>
<body>
    <script type="text/javascript">
    var str= 'Hello World!'
    var listPropertiesMethods = Object.getOwnPropertyNames(str)
    console.log(listPropertiesMethods);
    </script>
</body>
</html>
  • javascript
  • object
  • methods
  • properties
Share Improve this question asked Jan 5, 2018 at 12:51 Federico GentileFederico Gentile 5,95012 gold badges59 silver badges117 bronze badges 4
  • @JonasW. I get empty array.... – Federico Gentile Commented Jan 5, 2018 at 12:58
  • oh right, doesnt work with Object.keys, but with getOwnPropertyNames – Jonas Wilms Commented Jan 5, 2018 at 12:59
  • @JonasW. ok but getOwnPropertyName is what I have used and doesn't return all the methods like am asking... I need to print out also the other methods like toUpperCase() for example – Federico Gentile Commented Jan 5, 2018 at 13:01
  • @JonasW. yeah sure :) – Federico Gentile Commented Jan 5, 2018 at 13:02
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3 Answers 3

Reset to default 9

Cause the properties you list (indexOf, ...) are not part of the string object itself, but are rather part of its prototype:

Object.getOwnPropertyNames(
 Object.getPrototypeOf("str")
)

You have just look at the proto-type of your object and you get what you want:

console.log(str.__proto__);

The Object.getOwnPropertyNames(obj) method returns only the properties of the obj (like length). You can use Object.getPrototypeOf(obj) to get a more plete list of methods/properties.

Ex.:

Object.getOwnPropertyNames("Test")

(5) ["0", "1", "2", "3", "length"]

Object.getPrototypeOf("Test")

String {"", formatUnicorn: ƒ, truncate: ƒ, splitOnLast: ƒ, contains: ƒ, length: 0, …}

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