How do I Convert a String into an Integer in JavaScript?

Try parseInt function:

var number = parseInt("10");

But there is a problem. If you try to convert "010" using parseInt function, it detects as octal number, and will return number 8. So, you need to specify a radix (from 2 to 36). In this case base 10.

parseInt(string, radix)

Example:

var result = parseInt("010", 10) == 10; // Returns true

var result = parseInt("010") == 10; // Returns false

There are two main ways to convert a string to a number in javascript. One way is to parse it and the other way is to change its type to a Number. All of the tricks in the other answers (e.g. unary plus) involve implicitly coercing the type of the string to a number. You can also do the same thing explicitly with the Number function.

Parsing

var parsed = parseInt("97", 10);

parseInt and parseFloat are the two functions used for parsing strings to numbers. Parsing will stop silently if it hits a character it doesn't recognise, which can be useful for parsing strings like "92px", but it's also somewhat dangerous, since it won't give you any kind of error on bad input, instead you'll get back NaN unless the string starts with a number. Whitespace at the beginning of the string is ignored. Here's an example of it doing something different to what you want, and giving no indication that anything went wrong:

var widgetsSold = parseInt("97,800", 10); // widgetsSold is now 97

It's good practice to always specify the radix as the second argument. In older browsers, if the string started with a 0, it would be interpreted as octal if the radix wasn't specified which took a lot of people by surprise. The behaviour for hexadecimal is triggered by having the string start with 0x if no radix is specified, e.g. 0xff. The standard actually changed with ecmascript 5, so modern browsers no longer trigger octal when there's a leading 0 if no radix has been specified. parseInt understands radixes up to base 36, in which case both upper and lower case letters are treated as equivalent.

Changing the Type of a String to a Number

All of the other tricks mentioned above that don't use parseInt, involve implicitly coercing the string into a number. I prefer to do this explicitly,

var cast = Number("97");

This has different behavior to the parse methods (although it still ignores whitespace). It's more strict: if it doesn't understand the whole of the string than it returns NaN, so you can't use it for strings like 97px. Since you want a primitive number rather than a Number wrapper object, make sure you don't put new in front of the Number function.

Obviously, converting to a Number gives you a value that might be a float rather than an integer, so if you want an integer, you need to modify it. There are a few ways of doing this:

var rounded = Math.floor(Number("97.654"));  // other options are Math.ceil, Math.round
var fixed = Number("97.654").toFixed(0); // rounded rather than truncated
var bitwised = Number("97.654")|0;  // do not use for large numbers

Any bitwise operator (here I've done a bitwise or, but you could also do double negation as in an earlier answer or a bitshift) will convert the value to a 32bit integer, and most of them will convert to a signed integer. Note that this will not do want you want for large integers. If the integer cannot be represented in 32bits, it will wrap.

~~"3000000000.654" === -1294967296
// This is the same as
Number("3000000000.654")|0
"3000000000.654" >>> 0 === 3000000000 // unsigned right shift gives you an extra bit
"300000000000.654" >>> 0 === 3647256576 // but still fails with larger numbers

To work correctly with larger numbers, you should use the rounding methods

Math.floor("3000000000.654") === 3000000000
// This is the same as
Math.floor(Number("3000000000.654"))

Bear in mind that all of these methods understand exponential notation, so 2e2 is 200 rather than NaN. Also, Number understands "Infinity", while the parse methods don't.

Custom

It's unlikely that either of these methods do exactly what you want. For example, usually I would want an error thrown if parsing fails, and I don't need support for Infinity, exponentials or leading whitespace. Depending on your usecase, sometimes it makes sense to write a custom conversion function.

Always check that the output of Number or one of the parse methods is the sort of number you expect. You will almost certainly want to use isNaN to make sure the number is not NaN (usually the only way you find out that the parse failed).

ParseInt() and + are different

parseInt("10.3456") // returns 10

+"10.3456" // returns 10.3456

Try parseInt.

var number = parseInt("10", 10); //number will have value of 10.

I posted the wrong answer here, sorry. fixed.

This is an old question, but I love this trick:

~~"2.123"; //2
~~"5"; //5

The double bitwise negative drops off anything after the decimal point AND converts it to a number format. I've been told it's slightly faster than calling functions and whatnot, but I'm not entirely convinced.

EDIT: Another method I just saw here (a question about the javascript >>> operator, which is a zero-fill right shift) which shows that shifting a number by 0 with this operator converts the number to a uint32 which is nice if you also want it unsigned. Again, this converts to an unsigned integer, which can lead to strange behaviors if you use a signed number.

"-2.123" >>> 0; // 4294967294
"2.123" >>> 0; // 2
"-5" >>> 0; // 4294967291
"5" >>> 0; // 5

Though and old question, but maybe this can be helpful to someone.

I use this way of converting string to int number

var str = "25";       // string
var number = str*1;   // number

So, when multiplying by 1, the value does not change, but js automatically returns a number.

But as it is shown below, this should be used if you are sure that the str is a number, otherwise it will return NaN - not a number.

you can create simple function to use, e.g.

function toNumber(str) {
   return str*1;
}

Also as a side note: Mootools has the function toInt() which is used on any native string (or float (or integer)).

"2".toInt()   // 2
"2px".toInt() // 2
2.toInt()     // 2

Beware if you use parseInt to convert a float in scientific notation! For example:

parseInt("5.6e-14") 

will result in

5 

instead of

0

By using parsing method of JavaScript, you can convert string to integer:

var number = parseInt("11112");