Adding numbers with Javascript

Question

Easy question: I'm trying to add a number to an array like this:

sorted[4][2]+=nbrMvt[i];

but it adds the two numbers as if they were strings. The output just puts the numbers one beside the other... I have tried these methods:

sorted[4][2]+=parseInt(nbrMvt[i]);
sorted[4][2]=sorted[4][2]+nbrMvt[i];
sorted[4][2]=parseInt(sorted[4][2])+parseInt(nbrMvt[i]);

But none of them work.

[EDIT]

Ok, here is how I created my array:

var sorted = MultiDimensionalArray(13,4);

I then atribute string values to the sorted[x][0...12]
the last example gives me "NaNNaNNaNNaN"

 function MultiDimensionalArray(iRows,iCols)
 {
 var i;
 var j;
 var a = new Array(iRows);
 for (i=0; i < iRows; i++)
 {
 a[i] = new Array(iCols);
 for (j=0; j < iCols; j++)
 {
 a[i][j] = "";
 }
 }
 return(a);
 } 

(btw, what should I understand from the vote down on my question?)

• Thom Wiggers: Did you by any chance define the numbers in the array as "1" ?
• Chad: Lets have a little more context about how you are creating/filling your sorted variable. More than likely it's values are strings, causing the += to be concatenation.
• David Hedlund: @Chad: agreed. Off the top of my head, I can't think of anything that would explain why the last one wouldn't be working.
• Chad: What the hell is MultiDimensionalArray(13,4). Are you using a framework?
• sebastien leblanc: Chad you found my problem: "What the hell is MultiDimensionalArray(13,4)" I wrote a function that created the array and defined everything as a string. You can write an answer if you want me to mark it as my chosen answer...

Answer 1

You may not have set some value (perhaps i === null or somthing) ... But this works:

var sorted = [], 
nbrMvt = [],
i = 0;
// set up arrays and populate just enough values...
nbrMvt[i] = 40;
sorted[4] = [];
sorted[4][2] = 2;
sorted[4][2]=parseInt(sorted[4][2])+parseInt(nbrMvt[i]);
document.write(sorted[4][2]);

• Chad: Here is a jsFiddle of his code working as expected (with assumptions). Without more context a clear answer can't really be developed.

Answer 2

Your MultiDimensionalArray(iRows,iCols) function is defining the array contents as strings. When you try to add a number to an element in the array like: sorted[4][2] += 2 it is just concatenating to that string.

However the following should still work, even in that instance:

sorted[4][2] = parseInt(sorted[4][2])+parseInt(nbrMvt[i]);

Unless nbrMvt[i] is in an invalid format, causing parseInt() to return NaN. Which would make the sum also NaN.

Here is jsFiddle of working code similar to yours, with a small rewrite to your MultiDimensionalArray() function.

• sebastien leblanc: I get that it should still work, but it doesn't... I fixed it by changing the line a[i][j] = ""; by a[i][j] = 0; in my MultiDimensionalArray function. Thank you :)
• Chad: parseInt("") is NaN. So your initial value breaks the sum of those two numbers.

Answer 3

If you x+=4 you get NaN in x if it was null or undefined before.

It is good to fill thing you will += with number 0 first.

If you x+=4 you get "104" in x if it was string "10" before, not a number 10. If you x+=y you get "104" in x even if x was previously number 10 but y is string "4".

It is good to explicitly cast to number (using +foo; that is unary plus, not the addition operator, the shortest way to force number coercion in Javascript) if you want to have number arithmetics.