Can anyone explain why these operations yield these results:
(I understand the first one is somehow related to strings being based on arrays but what does 'based on' mean here, how does it work internally)
[] + [] = ""
[] - []= 0
[] + {} = "[object Object]"
[] - {} = NaN
{} + {} = NaN
{} - {} = NaN
{} + 1 = 1
When using the + operator javascript will attempt to convert the elements being added together first into a string, then into an int. When you cast an empty array to a string you get "" therefore "" + "" = ""
[] + [] = "" // equates to "" + "" = ""
When using the - operator javascript will attempt to convert the element into integers. Empty arrays cast into integers will product 0 so 0 - 0 = 0
[] - []= 0 // equates to 0 - 0 = 0
Same thing here, the empty array is being converted to "" and the object is being converted to "[object Object]" because of the concatenation with the empty string the result is "" + "[object Object]" = "[object Object]"
[] + {} = "[object Object]" // equates to "" + "[object Object]" = "[object Object]"
{} cannot be cast to an int so is instead cast to undefined and 0 - undefined = NaN
[] - {} = NaN // equates to 0 - undefined = NaN
When an expressions starts with an empty object literal javaScript interprets the first {} as an empty code block and ignores it so evaluates the following expressions as + {} which is NaN
{} + {} = NaN // equates to + {} = NaN
{} - {} = NaN // equates to - {} = NaN
{} + 1 = 1 // equates to + 1 = 1
- {} results in NaN not undefined.
{} is undefined so it is the same as writing - undefined which is NaNundefined? Number({}) also returns NaN.{} and {foo: "bar", baz: "qux"}. The first one will output "undefined" the second will throw an error unless you store it to a variable. When the javascript engine encounters an object literal on the left side of an expression it ignores it as an empty code block