JavaScript - concat two numbers and treat the result as a number

Question

here's the code I'm struggling with. I'd like to concat the two inputs together and keep the result as an integer (number in JS's case).

var secsVal = -1;
function valueAssign(i) {

    if (secsVal == -1){

        document.getElementById("countdown").value = i;
        document.getElementById("countdown").innerHTML = (i);

        secsVal = i;
    }
    else {      
        secsVal = "" + secsVal + i;//concatenating first value of i to the second.
        secsVal = secsVal.map(Number);//trying to convert back to num, but I think map() needs to see an array, which I don't think I got here.

        document.getElementById("countdown").value = secsVal;
        document.getElementById("countdown").innerHTML = (secsVal);//I want to replace the first displayed digit here, with the new (concatenated) number.
    }
}

Not sure I understand your requirements. In HTML all you can store is text (not JavaScript data types like numbers or dates). — Álvaro González, Oct 24 '16 at 08:26

score 2 · Accepted Answer · answered Oct 24 '16 at 08:27

2

It makes no sense to use a number for a value in an input tag. The type is always a string.

To convert to number use either Number or an unary +

secsVal = Number(secsVal);

or

secsVal = +secsVal;

answered Oct 24 '16 at 08:27

Nina Scholz

376,160
25
347
392

score 1 · Answer 2 · answered Oct 24 '16 at 08:26

1

Try this

secsVal = +("" + secsVal + i);

answered Oct 24 '16 at 08:26

Niyoko

7,512
4
32
59

score 0 · Answer 3 · answered Oct 24 '16 at 08:26

secsVal = Number('' + secsVal + i)   // explicit cast to number
secsVal = +('' + secsVal + i)        // implicit cast to number
secsVal = parseInt('' + secsVal + i) // explicit cast to integer
secsVal = ~~('' + secsVal + i)       // implicit cast to integer

score 0 · Answer 4 · answered Oct 24 '16 at 08:28

Simply use +secsVal

var secsVal = -1;
function valueAssign(i) {

    if (secsVal == -1){

        document.getElementById("countdown").value = i;
        document.getElementById("countdown").innerHTML = (i);

        secsVal = i;
    }
    else {      
        secsVal = "" + secsVal + i;
        console.log(typeof secsVal);//secsVal is a string
        
        secsVal = +secsVal;
        console.log(typeof secsVal); //secsVal is now a number

        document.getElementById("countdown").value = secsVal;
    }
}

<input type="number" id="countdown"/>
<button onclick="valueAssign(5)">Click</button>

score 0 · Answer 5 · answered Oct 24 '16 at 08:31

0

How about parsing the String?

"The parseInt() function parses a string and returns an integer." http://www.w3schools.com/jsref/jsref_parseint.asp

answered Oct 24 '16 at 08:31

rob2universe

7,059
39
54

JavaScript - concat two numbers and treat the result as a number

5 Answers5