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    parseInt Redirect 1

    Summary

    The parseInt() function parses a string argument and returns an integer of the specified radix or base.

    Syntax

    parseInt(string, radix);

    Parameters

    string
    The value to parse. If string is not a string, then it is converted to one. Leading whitespace in the string is ignored.
    radix
    An integer that represents the radix of the above mentioned string. Always specify this parameter to eliminate reader confusion and to guarantee predictable behavior. Different implementations produce different results when a radix is not specified.

    Description

    The parseInt function converts its first argument to a string, parses it, and returns an integer or NaN. If not NaN, the returned value will be the decimal integer representation of the first argument taken as a number in the specified radix (base). For example, a radix of 10 indicates to convert from a decimal number, 8 octal, 16 hexadecimal, and so on. For radices above 10, the letters of the alphabet indicate numerals greater than 9. For example, for hexadecimal numbers (base 16), A through F are used.

    If parseInt encounters a character that is not a numeral in the specified radix, it ignores it and all succeeding characters and returns the integer value parsed up to that point. parseInt truncates numbers to integer values. Leading and trailing spaces are allowed.

    If radix is undefined or 0 (or absent), JavaScript assumes the following:

    • If the input string begins with "0x" or "0X", radix is 16 (hexadecimal) and the remainder of the string is parsed.
    • If the input string begins with "0", radix is eight (octal) or 10 (decimal).  Exactly which radix is chosen is implementation-dependent.  ECMAScript 5 specifies that 10 (decimal) is used, but not all browsers support this yet.  For this reason always specify a radix when using parseInt.
    • If the input string begins with any other value, the radix is 10 (decimal).

    If the first character cannot be converted to a number, parseInt returns NaN.

    For arithmetic purposes, the NaN value is not a number in any radix. You can call the isNaN function to determine if the result of parseInt is NaN. If NaN is passed on to arithmetic operations, the operation results will also be NaN.

    To convert number to its string literal in a particular radix use intValue.toString(radix).

    Examples

    Example: Using parseInt

    The following examples all return 15:

    parseInt(" 0xF", 16);
    parseInt(" F", 16);
    parseInt("17", 8);
    parseInt(021, 8);
    parseInt("015", 10);
    parseInt(15.99, 10);
    parseInt("FXX123", 16);
    parseInt("1111", 2);
    parseInt("15*3", 10);
    parseInt("15e2", 10);
    parseInt("15px", 10);
    parseInt("12", 13);
    

    The following examples all return NaN:

    parseInt("Hello", 8); // Not a number at all
    parseInt("546", 2);   // Digits are not valid for binary representations
    

    The following examples all return -15:

    parseInt("-F", 16);
    parseInt("-0F", 16);
    parseInt("-0XF", 16);
    parseInt(-15.1, 10)
    parseInt(" -17", 8);
    parseInt(" -15", 10);
    parseInt("-1111", 2);
    parseInt("-15e1", 10);
    parseInt("-12", 13);
    

    The following example returns 224:

    parseInt("0e0", 16);
    

    Octal interpretations with no radix

    Although discouraged by ECMAScript 3 and forbidden by ECMAScript 5, many implementations interpret a numeric string beginning with a leading 0 as octal. The following may have an octal result, or it may have a decimal result.  Always specify a radix to avoid this unreliable behavior.

    parseInt("0e0"); // 0
    parseInt("08"); // 0, '8' is not an octal digit.
    

    ECMAScript 5 removes octal interpretation

    The ECMAScript 5 specification of the function parseInt no longer allows implementations to treat Strings beginning with a 0 character as octal values. ECMAScript 5 states:

    The parseInt function produces an integer value dictated by interpretation of the contents of the string argument according to the specified radix. Leading white space in string is ignored. If radix is undefined or 0, it is assumed to be 10 except when the number begins with the character pairs 0x or 0X, in which case a radix of 16 is assumed. If radix is 16, number may also optionally begin with the character pairs 0x or 0X.

    This differs from ECMAScript 3, which discouraged but allowed octal interpretation.

    Many implementations have not adopted this behavior as of 2013, and because older browsers must be supported, always specify a radix.

    A stricter parse function

    It is sometime usefull to have a stricter way to parse int values, regular expressions can help:

    filterInt = function (value) {
      if(/^(\-|\+)?([0-9]+|Infinity)$/.test(value))
        return Number(value);
      return NaN;
    }
    
    console.log(filterInt('421'));               // 421
    console.log(filterInt('-421'));              // -421
    console.log(filterInt('+421'));              // 421
    console.log(filterInt('Infinity'));          // Infinity
    console.log(filterInt('421e+0'));            // NaN
    console.log(filterInt('421hop'));            // NaN
    console.log(filterInt('hop1.61803398875'));  // NaN
    console.log(filterInt('1.61803398875'));     // NaN
    

    Specifications

    Specification Status Comment
    ECMAScript 1st Edition. Standard Initial definition.
    ECMAScript Language Specification 5.1th Edition (ECMA-262) Standard  
    ECMAScript Language Specification 6th Edition (ECMA-262) Draft  

    Browser compatibility

    Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
    Basic support (Yes) (Yes) (Yes) (Yes) (Yes)
    Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
    Basic support (Yes) (Yes) (Yes) (Yes) (Yes) (Yes)

    See also

    Document Tags and Contributors

    Contributors to this page: Sheppy
    Last updated by: Sheppy,