What is {} + {} in JavaScript? [duplicate]

Question

1st Part:

Because When you are adding two arrays, everything works as expected:

 [] + []     //output:''

Adding an array and an object also conforms to our expectations:

 [] + {}
output:'[object Object]'

{} + {} in JavaScript is NaN ?
and this is unexpected result so what is the reason behind this?

2nd part:

In string comparison without prefix 0, 3 is greater than 12:

"3" > "12"
: true

With padding, everything works correctly:

 "03" > "12"
: false

Is prefix 0 compulsory for string comparision?What is the reason for adding prefix 0 ?

Answer 1

1. {} + {} is interpreted as the empty block {} followed by the expression + {}. {} has no numerical value, so it yields NaN. If you force it to be evaluated as an expression like ({} + {}), you'll get [object Object][object Object].

2. They're strings, so they'll be compared lexicographically. If you want to compare them as numbers, parse them first using parseInt or parseFloat.

Answer 2

the first part

1-

when you add two arrays you take the primitive value for each and arrays can be converted to strings like the following [1,2,3,4].toString() //=> 1,2,3,4 so the two emty arrays generates to empty strings and the concatenation between them generates empty string.

2- when for the second when you add empty string with object, you are converting the object to string and as shown the string value of an object is [object Object]

3-

when you add two objects, in the way shown you are just converting an object to number by the + check this question

Part Two

String compare is made letter by letter from left to right and as soon as there is a deference the return value is determined ignoring the string length like the following

"3" > "12"

"3" in ASCII is bigger than "1" so the return is TRUE

"03" > "12"

"0" in ASCII is smaller than "1" so the return is False