Data Type Testing

How is testing done?

To test the equality or inequality of two primitive data values, we always use the triple equality symbol (=== and !==) instead of the double equality symbol (== and !=). Otherwise, for instance, the number 2 would be the same as the string "2" since the condition 2 == "2" evaluates to true in JavaScript.

Assigning an empty array literal, as in var a = [], is the same as invoking the Array() constructor without arguments, as in var a = new Array(). Assigning an empty object literal, as in var o = {}, is the same as invoking the Object() constructor without arguments, as in var o = new Object().

Notice, however, that an empty object literal {} is not really an empty object, as it contains property slots and method slots inherited from Object.prototype. So, a truly empty object (without any slots) has to be created with null as the prototype, like in var emptyObject = Object.create(null).