JavaScript String and Number Conversion

How to convert a string to an integer in JavaScript

The simplest way would be to use the native Number function:

var x = Number("1000")

If that doesn't work for you, then there are the parseInt, unary plus, parseFloat with floor, and Math.round methods.

parseInt()

var x = parseInt("1000", 10); // You want to use radix 10
    // So you get a decimal number even with a leading 0 and an old browser ([IE8, Firefox 20, Chrome 22 and older][1])

Unary plus

If your string is already in the form of an integer:

var x = +"1000";

floor()

If your string is or might be a float and you want an integer:

var x = Math.floor("1000.01"); // floor() automatically converts string to number

Or, if you're going to be using Math.floor several times:

var floor = Math.floor;
var x = floor("1000.01");

parseFloat()

If you're the type who forgets to put the radix in when you call parseInt, you can use parseFloat and round it however you like. Here I use floor.

var floor = Math.floor;
var x = floor(parseFloat("1000.01"));

round()

Interestingly, Math.round (like Math.floor) will do a string to number conversion, so if you want the number rounded (or if you have an integer in the string), this is a great way, maybe my favorite:

var round = Math.round;
var x = round("1000"); // Equivalent to round("1000", 0)

What's the best way to convert a number to a string in JavaScript?

like this:

var foo = 45;
var bar = '' + foo;

Actually, even though I typically do it like this for simple convenience, over 1,000s of iterations it appears for raw speed there is an advantage for .toString()

See Performance tests here (not by me, but found when I went to write my own):
http://jsben.ch/#/ghQYR

Fastest based on the JSPerf test above: str = num.toString();

It should be noted that the difference in speed is not overly significant when you consider that it can do the conversion any way 1 Million times in 0.1 seconds.

Update: The speed seems to differ greatly by browser. In Chrome num + '' seems to be fastest based on this test http://jsben.ch/#/ghQYR

Update 2: Again based on my test above it should be noted that Firefox 20.0.1 executes the .toString() about 100 times slower than the '' + num sample.

JavaScript string and number conversion

You want to become familiar with parseInt() and toString().

And useful in your toolkit will be to look at a variable to find out what type it is—typeof:

<script type="text/javascript">
    /**
     * print out the value and the type of the variable passed in
     */

    function printWithType(val) {
        document.write('<pre>');
        document.write(val);
        document.write(' ');
        document.writeln(typeof val);
        document.write('</pre>');
    }

    var a = "1", b = "2", c = "3", result;

    // Step (1) Concatenate "1", "2", "3" into "123"
    // - concatenation operator is just "+", as long
    //   as all the items are strings, this works
    result = a + b + c;
    printWithType(result); //123 string

    // - If they were not strings you could do
    result = a.toString() + b.toString() + c.toString();
    printWithType(result); // 123 string

    // Step (2) Convert "123" into 123
    result = parseInt(result,10);
    printWithType(result); // 123 number

    // Step (3) Add 123 + 100 = 223
    result = result + 100;
    printWithType(result); // 223 number

    // Step (4) Convert 223 into "223"
    result = result.toString(); //
    printWithType(result); // 223 string

    // If you concatenate a number with a 
    // blank string, you get a string    
    result = result + "";
    printWithType(result); //223 string
</script>

How to convert a string to number in TypeScript?

Exactly like in JavaScript, you can use the parseInt or parseFloat functions, or simply use the unary + operator:

var x = "32";
var y: number = +x;

All of the mentioned techniques will have correct typing and will correctly parse simple decimal integer strings like "123", but will behave differently for various other, possibly expected, cases (like "123.45") and corner cases (like null).

Table taken from this answer

What's the fastest way to convert String to Number in JavaScript?

There are 4 ways to do it as far as I know.

Number(x);
parseInt(x, 10);
parseFloat(x);
+x;

By this quick test I made, it actually depends on browsers.

https://jsben.ch/NnBKM

Implicit marked the fastest on 3 browsers, but it makes the code hard to read… So choose whatever you feel like it!

---

Related Topics