Why adding an array to a number returns a string?

Question

var array = [1,2,4];

array+1  //gives '1,2,41'.

Can anyone explain this behavior?

Answer 1

Can anyone explain this behavior?

This answer attempts to explain this behavior in terms of specification.

According to spec , during time evaluation, +both expressions (left and right) are converted to their primitive values.

7. Let lprim be ToPrimitive (lval).
8. Let rprim be ToPrimitive (rval).

toPrimitive tries to pass hint:number(after the call during arithmetic evaluation) to OrdinaryToPrimitive

3. "", . methodNames "toString", "valueOf" ".
4. Else,
   . methodNames " "valueOf", "toString" ".//

, 4a) , .

[1,2,4] + 1 = > [1,2,4].toString() + "1" = > "1,2,4" + "1" = > () "1,2,41"

Answer 2

- , .

Answer 3

+ javascipt (var array), , - .

[1,2,4] 1,2,4. , 1,2,4, 1, 1,2,41

Answer 4

? [2,3,5]?

, 1 ( ). , 1 ?

JS , . , "" 2 ( ), .

, +1 . :

for (var i=array .length; i--;) {
    array [i]++;
}

array = array.map(function(e) {return '#' + e});

ES6

array = array.map(i => i + 1);

Answer 5

, .

Both an array and a number can be converted to a string, this is called coercion .

If you want to add 1to an array, you can do this:

var array = [1,2,4];
array.push(1);