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Other References

CSSStyleDeclaration JS Conversion


JavaScript Boolean prototype

Example

Make a new method for JavaScript booleans:

Boolean.prototype.myColor = function() {
  if (this.valueOf() == true) {
    return "green";
  } else {
    return = "red";
  }
};

Create a boolean, then call myColor():

let a = true;
let color = a.myColor();
Try it Yourself »

Definition and Usage

prototype allows you to add new properties and methods to booleans.

prototype is a property available with all JavaScript objects.


Syntax

Boolean.prototype.name = value

Warning

You are not advised to change the prototype of an object that you do not control.

You should not change the prototype of built in JavaScript datatypes like:

  • Numbers
  • Strings
  • Arrays
  • Dates
  • Booleans
  • Function
  • Objects

Only change the prototype of your own objects.

The prototype Property

The JavaScript prototype property allows you to add new properties to objects:

Example

function Person(first, last, age, eyecolor) {
  this.firstName = first;
  this.lastName = last;
  this.eyeColor = eyecolor;
}

Person.prototype.nationality = "English";
Try it Yourself »

Browser Support

prototype is an ECMAScript1 (ES1) feature.

ES1 (JavaScript 1997) is fully supported in all browsers:

Chrome Edge Firefox Safari Opera IE
Yes Yes Yes Yes Yes Yes