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Showing content from https://webplatform.github.io/docs/javascript/Object/keys below:

keys · WebPlatform Docs

keys Summary

Returns the names of the enumerable properties and methods of an object.

Syntax

Object.keys( object )

object: Required. The object that contains the properties and methods. This can be an object that you created or an existing Document Object Model (DOM) object.

Return Value

An array that contains the names of the enumerable properties and methods of the object.

Examples

The following example creates an object that has three properties and a method. It then uses the keys method to get the properties and methods of the object.


 function Pasta(grain, width, shape) {
     this.grain = grain;
     this.width = width;
     this.shape = shape;

     
     this.toString = function () {
         return (this.grain + ", " + this.width + ", " + this.shape);
     }
 }

 
 var spaghetti = new Pasta("wheat", 0.2, "circle");

 
 var arr = Object.keys(spaghetti);
 document.write (arr);

The following example displays the names of all enumerable properties that start with the letter “g” in the Pasta object.


 function Pasta(grain, width, shape) {
     this.grain = grain;
     this.width = width;
     this.shape = shape;
 }

 var polenta = new Pasta("corn", 1, "mush");

 var keys = Object.keys(polenta).filter(CheckKey);
 document.write(keys);

 
 function CheckKey(value) {
     var firstChar = value.substr(0, 1);
     if (firstChar.toLowerCase() == "g")
         return true;
     else
         return false;
 }

Remarks

The keys method returns only the names of enumerable properties and methods. To return the names of both enumerable and non-enumerable properties and methods, you can use Object.getOwnPropertyNames Function.

For information about the enumerable attribute of a property, see Object.defineProperty Function and Object.getOwnPropertyDescriptor Function.

Exceptions

If the value supplied for the object argument is not the name of an object, a TypeError exception is thrown.