Why should you not use Number as a constructor? [duplicate]

by

In addition to breaking === and typeof returning “object”, using the Number constructor also changes the way the value is used in boolean contexts. Since “new Number(0)” is an object, not a literal value, it evaluates as “true” because it is not null. So for example:

var n1 = 0;
var n2 = new Number(0);

n1 == n2  // true
n1 === n2 // false
if (n1) {
    // Doesn't execute
}
if (n2) {
    // Does execute, because n2 is an object that is not null
}

Even worse than breaking === between number literals and Number objects, == doesn’t even work between two Number objects (at least not in the intuitive way — they test for identity, not equality).

var n1 = new Number(3);
var n2 = new Number(3);

alert(n1 == n2); // false
alert(n1 === n2); // false

More Related Contents:

  1. Use of .apply() with ‘new’ operator. Is this possible?
  2. Understanding prototypal inheritance in JavaScript
  3. JSLint Error: Unexpected ‘this’
  4. OO Javascript constructor pattern: neo-classical vs prototypal
  5. What is the reason to use the ‘new’ keyword at Derived.prototype = new Base
  6. Advantages of using prototype, vs defining methods straight in the constructor? [duplicate]
  7. What is the difference between `new Object()` and object literal notation?
  8. What values can a constructor return to avoid returning this?
  9. How to get a JavaScript object’s class?
  10. The value of “this” within the handler using addEventListener
  11. Anonymous class instance —- is it a bad idea?
  12. Class vs. static method in JavaScript
  13. JavaScript: Class.method vs. Class.prototype.method
  14. Difference of the value, prototype and property
  15. JavaScript private methods
  16. (…()) vs. (…)() in javascript closures [duplicate]
  17. JavaScript function order: why does it matter?
  18. How to call a parent method from child class in javascript?
  19. Javascript dynamically invoke object method from string
  20. How to dynamically set a function/object name in Javascript as it is displayed in Chrome
  21. JSLint “insecure ^” in regular expression
  22. Asynchronous constructor
  23. Why is JSHINT complaining that this is a strict violation?
  24. ES6 – Call static method within a class
  25. Preserve ‘this’ reference in javascript prototype event handler [duplicate]
  26. JavaScript override methods
  27. Duck Typing in Javascript
  28. Why aren’t methods of an object created with class bound to it in ES6?
  29. What does the JSLint error ‘body of a for in should be wrapped in an if statement’ mean?
  30. JSLint: Using a function before it’s defined error

Leave a Comment