What is the difference between parseInt and Number

Question

How do parseInt   and Number   behave differently when converting strings to numbers

User · Answer

Its a good idea to stay away from parseInt and use Number and Math.round unless you need hex or octal. Both can use strings. Why stay away from it?

parseInt(0.001, 10)
0

parseInt(-0.0000000001, 10)
-1

parseInt(0.0000000001, 10)
1

parseInt(4000000000000000000000, 10)
4

It completly butchers really large or really small numbers. Oddly enough it works normally if these inputs are a string.

parseInt("-0.0000000001", 10)
0

parseInt("0.0000000001", 10)
0

parseInt("4000000000000000000000", 10)
4e+21

Instead of risking hard to find bugs with this and the other gotchas people mentioned, I would just avoid parseInt unless you need to parse something other than base 10. Number, Math.round, Math.foor, and .toFixed(0) can all do the same things parseInt can be used for without having these types of bugs.

If you really want or need to use parseInt for some of it's other qualities, never use it to convert floats to ints.

User · Answer

parseInt   -  Parses a number to specified redix   Number  -  Converts the specified value to its numeric equivalent or NaN if it fails to do so   Hence for converting some non-numeric value to number we should always use Number   function   eg   Number      0 parseInt      NaN  Number  123    123 parseInt  123    123  Number  123ac     NaN as it is a non numeric string parsInt  123ac     123 it parse decimal number outof string  Number true   1 parseInt true    NaN   There are various corner case to parseInt   functions as it does redix conversion  hence we should avoid using parseInt   function for coersion purposes   Now  to check weather the provided value is Numeric or not we should use nativeisNaN   function

User · Answer

Summary   parseInt      Takes a string as a first argument  the radix  An integer which is the base of a numeral system e g  decimal 10 or binary 2  as a second argument The function returns a integer number  if the first character cannot be converted to a number NaN will be returned  If the parseInt   function encounters a non numerical value  it will cut off the rest of input string and only parse the part until the non numerical value  If the radix is undefined or 0  JS will assume the following    If the input string begins with  0x  or  0X   the radix is 16  hexadecimal   the remainder of the string is parsed into a number  If the input value begins with a 0 the radix can be either 8  octal  or 10  decimal   Which radix is chosen is depending on JS engine implementation  ES5 specifies that 10 should be used then  However  this is not supported by all browsers  therefore always specify radix if your numbers can begin with a 0  If the input value begins with any number  the radix will be 10    Number      The Number   constructor can convert any argument input into a number  If the Number   constructor cannot convert the input into a number  NaN will be returned  The Number   constructor can also handle hexadecimal number  they have to start with 0x    Example    x000D   x000D  console log parseInt  0xF   16        15 x000D   x000D     z is no number  it will only evaluate 0xF  therefore 15 is logged x000D  console log parseInt  0xFz123   16    x000D   x000D     because the radix is 10  A is considered a letter not a number  like in Hexadecimal  x000D     Therefore  A will be cut off the string and 10 is logged x000D  console log parseInt  10A   10        10 x000D   x000D     first character isnot a number  therefore parseInt will return NaN x000D  console log parseInt  a1213   10    x000D   x000D   x000D  console log   n    x000D   x000D   x000D     start with 0X  therefore Number will interpret it as a hexadecimal value x000D  console log Number  0x11     x000D   x000D     Cannot be converted to a number  NaN will be returned  notice that x000D     the number constructor will not cut off a non number part like parseInt does x000D  console log Number  123A     x000D   x000D     scientific notation is allowed x000D  console log Number  152e-1         15 21 x000D   x000D   x000D

User · Answer

If you are looking for performance then probably best results you ll get with bitwise right shift  10  gt  gt 0  Also multiply   10    1  or not not     10    All of them are much faster of Number and parseInt  They even have  feature  returning 0 for not number argument  Here are Performance tests

User · Answer

I always use parseInt  but beware of leading zeroes that will force it into octal mode

User · Answer

One minor difference is what they convert of undefined or null   Number   Or Number null     returns 0   while   parseInt   Or parseInt null     returns NaN

User · Answer

parseInt converts to a integer number  that is  it strips decimals  Number does not convert to integer

User · Answer

I found two links of performance compare among several ways of converting string to int   parseInt str 10      parseFloat str  str  lt  lt  0  str str 1  str-0 Number str    http   jsben ch   zGJHM  http   phrogz net js string to number html

User · Answer

Well  they are semantically different  the Number constructor called as a function performs type conversion and parseInt performs parsing  e g      parsing  parseInt  quot 20px quot             20 parseInt  quot 10100 quot   2        20 parseInt  quot 2e1 quot              2     type conversion Number  quot 20px quot             NaN Number  quot 2e1 quot              20  exponential notation  Also parseInt will ignore trailing characters that don t correspond with any digit of the currently used base  The Number constructor doesn t detect implicit octals  but can detect the explicit octal notation  Number  quot 010 quot               10 Number  quot 0o10 quot              8  explicit octal  parseInt  quot 010 quot             8  implicit octal parseInt  quot 010 quot   10        10  decimal radix used  And it can handle numbers in hexadecimal notation  just like parseInt  Number  quot 0xF quot         15 parseInt  quot 0xF quot      15  In addition  a widely used construct to perform Numeric type conversion  is the Unary   Operator  p  72   it is equivalent to using the Number constructor as a function    quot 2e1 quot        20   quot 0xF quot        15   quot 010 quot        10

User · Answer

typeof parseInt  123     gt  number typeof Number  123     gt  number typeof new Number  123     gt  object  Number primitive wrapper object    first two will give you better performance as it returns a primitive instead of an object

User · Answer

Because none mentioned  when using Number and parseInt with numeric separator  they also behave differently  const num1   5 0     50 const num2   Number 5 0      50 const num3   Number  quot 5 0 quot       NaN const num4   parseInt 5 0      50 const num5   parseInt  quot 5 0 quot       5

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

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