Objects and arrays addition

Question

Can anyone explain to me how the results of the following was evaluated?

{} + {} // NaN
[] + {} // \"[object Object]\"
{} + [] // 0
[] + [] // \"\"
         


        

Answer 1

Adding arrays with any object and its string representation always results in a join

For example:

[1] + [2] // is merged to "12", so [] + [] is an empty string ""

The same equals for your second example

['test'] + {} // "test[object Object]"

So an empty array plus an empty object will just return an [object Object]

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For adding to empty objects it's easy too:

Evaluate a simple empty object: {} // results in undefined

And adding two undefined values is NaN because there's no way you can make an addition on them.

Note: The return values depend on the implementation of JavaScript (i.e. in which Browser or Environment)

Also: What is {} + {} in JavaScript?