What is the difference between parseInt string and Number string in JavaScript

Question

What is the difference between parseInt string  and Number string  in JavaScript

User · Answer

The first one takes two parameters   parseInt string  radix    The radix parameter is used to specify which numeral system to be used  for example  a radix of 16  hexadecimal  indicates that the number in the string should be parsed from a hexadecimal number to a decimal number   If the radix parameter is omitted  JavaScript assumes the following    If the string begins with  0x   the radix is 16  hexadecimal  If the string begins with  0   the radix is 8  octal   This feature is deprecated If the string begins with any other value  the radix is 10     decimal    The other function you mentioned takes only one parameter   Number object    The Number   function converts the object argument to a number that represents the object s value   If the value cannot be converted to a legal number  NaN is returned

User · Answer

parseInt string  will convert a string containing non-numeric characters to a number  as long as the string begins with numeric characters   10px    gt  10   Number string  will return NaN if the string contains any non-numeric characters   10px    gt  NaN

User · Answer

Addendum to  sjngm s answer   They both also ignore whitespace   var foo        3        console log parseInt foo       3 console log Number foo       3

User · Answer

Addendum to  sjngm s answer       They both also ignore whitespace       var foo        3         console log parseInt foo       3   console log Number foo       3   It is not exactly correct  As sjngm wrote parseInt parses string to first number  It is true  But the problem is when you want to parse number separated with whitespace ie   12 345   In that case parseInt  12 345   will return 12 instead of 12345  So to avoid that situation you must trim whitespaces before parsing to number  My solution would be        var number parseInt  12 345  replace   s  g      10     Notice one extra thing I used in parseInt   function  parseInt  string  10  will set the number to decimal format  If you would parse string like  08  you would get 0 because 8 is not a octal number Explanation is here

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The parseInt function allows you to specify a radix for the input string and is limited to integer values   parseInt  Z   36      35   The Number constructor called as a function will parse the string with a grammar and is limited to base 10 and base 16    StringNumericLiteral         StrWhiteSpaceopt      StrWhiteSpaceopt StrNumericLiteral StrWhiteSpaceopt  StrWhiteSpace         StrWhiteSpaceChar StrWhiteSpaceopt  StrWhiteSpaceChar         WhiteSpace      LineTerminator  StrNumericLiteral         StrDecimalLiteral      HexIntegerLiteral  StrDecimalLiteral         StrUnsignedDecimalLiteral        StrUnsignedDecimalLiteral      - StrUnsignedDecimalLiteral  StrUnsignedDecimalLiteral         Infinity      DecimalDigits   DecimalDigitsopt ExponentPartopt        DecimalDigits ExponentPartopt          DecimalDigits ExponentPartopt  DecimalDigits         DecimalDigit      DecimalDigits DecimalDigit  DecimalDigit     one of     0 1 2 3 4 5 6 7 8 9  ExponentPart         ExponentIndicator SignedInteger  ExponentIndicator     one of     e E  SignedInteger         DecimalDigits        DecimalDigits      - DecimalDigits  HexIntegerLiteral         0x HexDigit      0X HexDigit      HexIntegerLiteral HexDigit  HexDigit     one of     0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E F

User · Answer

parseInt  123qwe     returns 123  Number  123qwe     returns NaN  In other words parseInt   parses up to the first non-digit and returns whatever it had parsed  Number   wants to convert the entire string into a number  which can also be a float BTW     EDIT  1  Lucero commented about the radix that can be used along with parseInt    As far as that is concerned  please see THE DOCTOR s answer below  I m not going to copy that here  the doc shall have a fair share of the fame         EDIT  2  Regarding use cases  That s somewhat written between the lines already  Use Number   in cases where you indirectly want to check if the given string completely represents a numeric value  float or integer  parseInt   parseFloat   aren t that strict as they just parse along and stop when the numeric value stops  radix    which makes it useful when you need a numeric value at the front  in case there is one   note that parseInt  hui   also returns NaN   And the biggest difference is the use of radix that Number   doesn t know of and parseInt   may indirectly guess from the given string  that can cause weird results sometimes

[javascript] What is the difference between parseInt(string) and Number(string) in JavaScript?

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