嵌套循环 var 声明

Question

I want to print this

1 2 3 4 5 
2 3 4 5 6 
3 4 5 6 7 
4 5 6 7 8 
5 6 7 8 9 

The code appears to look like this, after many guesses

var a=5;
for (var i = 1; i <= a; i++) {  
     var result="";
 for (var j = 1; j <= a; j++) {
    result +=(i+j - 1)+ " ";
   }
   console.log(result);
  }

But I still can't quite understand why if the var result declaration is in some other place (for example outside the loops) the result is completely different.

Answer 1

It is not the declaration, which is hoisted for var , but the first value for each row.

 var a = 5, result; for (var i = 1; i <= a; i++) { result = ""; for (var j = 1; j <= a; j++) { result += (i + j - 1) + " "; } console.log(result); }

Answer 2

You can take the declaration of result out of the loop as in:

var a = 5, result;
for (...
...

But you must clear it in each outer loop iteration or it will print an ever increasing row of repeated patterns per iteration.

Final code is:

var a = 5, result;

for (var i = 1; i <= a; i++) {
    result = ""; //Clearing happens here.
    for (var j = 1; j <= a; j++) {
        result += (i + j - 1) + " ";
    }
    console.log(result);
}