How to convert a string to number in TypeScript

Question

Given a string representation of a number  how can I convert it to number type in TypeScript   var numberString  string    1234   var numberValue  number      what should I do with  numberString

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typescript needs to know that our var a is going to ether be Number    String  export type StringOrNumber   number   string   export function toString  v  StringOrNumber     return    v        export function toNumber  v  StringOrNumber     return Number v      export function toggle  v  StringOrNumber     return typeof v      number       v     Number v

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For our fellow Angular users   Within a template  Number x  and parseInt x  throws an error  and  x has no effect  Valid casting will be x 1 or x 1

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There are a lot of you are having a problem to convert data types are difficult to solve in the ionic programming situations  because this very language is new  here I will detail instructions for the user to know how to convert data ionic types to string data type integer   In programming languages such as java  php  c  c        all can move data easily  then in ionic can also create for us data conversion is also an easy way not least in other programming languages   this mPosition   parseInt

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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

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You can follow either of the following ways   var str    54    var num    str    easy way by using   operator var num   parseInt str     by using the parseInt operation

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As shown by other answers here  there are multiple ways to do the conversion  Number  123      123   parseInt  123    parseFloat  123 45    I d like to mention one more thing on parseInt though  When using parseInt  it makes sense to always pass the radix parameter  For decimal conversion  that is 10  This is the default value for the parameter  which is why it can be omitted  For binary  it s a 2 and 16 for hexadecimal  Actually  any radix between and including 2 and 36 works  parseInt  123              123  don t do this  parseInt  123   10         123  much better   parseInt  1101   2         13 parseInt  0xfae3   16      64227  In some JS implementations  parseInt parses leading zeros as octal   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      MDN  The fact that code gets clearer is a nice side effect of specifying the radix parameter  Since parseFloat only parses numeric expressions in radix 10  there s no need for a radix parameter here  More on this   Why do we need to use radix   SO Question  SO Answer to  quot What is the difference between parseInt   and Number    quot

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Call the function with    convertstring  10 00    parseFloat string     It can be used to convert to float   toFixed 4     to how much decimals  parseInt str     It can be used to convert to integer  convertstring string       let number parsed  any   parseFloat string  toFixed 4      return number parsed

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There are inbuilt functions like parseInt    parseFloat   and Number   in Typescript  you can use those

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There are three ways   let a      12     let b   parseInt  12    10      10 means decimal number  let c   Number  12

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String to number conversion   In Typescript we convert a string to a number in the following ways    ParseInt    This function takes 2 arguments  the first is a string to parse  The second is the radix  the base in mathematical numeral systems  e g  10 for decimal and 2 for binary   It then returns the integer number  if the first character cannot be converted into a number  NaN will be returned  ParseFloat    Takes as an argument the value which we want to parse  and returns a floating point number  If the value cannot be converted to a number  NaN is returned    operator  The operator when used appropriately can coerce a string value into a number    Examples    x000D   x000D        parseInt      x000D   x000D     note that a whole number is returned  so it will round the number x000D  console log parseInt  51 023124     x000D   x000D     parseInt will  cut off  any part of the string which is not a number x000D  console log parseInt  5adfe1234     x000D   x000D     When the string starts with non number NaN is returned x000D  console log parseInt  z123     x000D   x000D  console log  --------    x000D   x000D        parseFloat      x000D   x000D     parses the string into a number and keeping the precision of the number x000D  console log typeof parseFloat  1 12321423     x000D   x000D     parseFloat will  cut off  any part of the string which is not a number x000D  console log parseFloat  5 5abc     x000D   x000D  console log  --------    x000D   x000D         operator      x000D   x000D  let myString    12345  x000D   x000D  console log typeof  myString   x000D   x000D  let myOtherString    10ab  x000D   x000D       operator will not cut off any  non number  string part and will return NaN x000D  console log  myOtherString   x000D   x000D   x000D    Which to use    Use ParseInt   when you want a string converted to an integer  However  the data type is still a float  since all number values are floating point values in TS  Also use this method when you need to specifiy the radix of the number you want to parse  Use ParseFloat   when you need to parse a string into a floating point number  You can use the   operator before a string to coerce it into a floating point number  The advantage of this is that the syntax is very short

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x000D   x000D  var myNumber  number   1200  x000D    convert to hexadecimal value x000D  console log myNumber toString 16      will return  4b0 x000D    Other way of converting to hexadecimal x000D  console log Math abs myNumber  toString 16      will return  4b0 x000D    convert to decimal value x000D  console log parseFloat myNumber toString    toFixed 2      will return  1200 00 x000D   x000D   x000D    Online Number Conversion Tool  Number Converter

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Here is a modified version of the StrToNumber function  As before     It allows an optional sign to appear in front or behind the numeric value   It performs a check to verify there is only one sign at the head or tail of the string  If an error occurs  a  passed  default value is returned     This response is a possible solution that is better suited to the initial question than my previous post    x000D   x000D     static StrToNumber val  string  defaultVal number   0   number x000D               x000D        let result number   defaultVal        x000D        if val    null   x000D           return result              x000D        if val length    0   x000D           return result        x000D        val   val trim    x000D        if val length    0   x000D           return result   x000D        let sign number   1       x000D           x000D             obtain sign from string  and place result in  sign  local variable  The Sign naturally defaults to positive x000D               1 for positive  -1 for negative  x000D             remove sign character from val   x000D                Note  before the function returns  the result is multiplied by the sign local variable to reflect the sign  x000D             error check for multiple sign characters x000D             error check to make sure sign character is at the head or tail of the string x000D                         x000D            x000D           let positiveSignIndex   val indexOf       x000D           let negativeSignIndex   val indexOf  -    x000D           let nTailIndex   val length-1  x000D              x000D              make sure both negative and positive signs are not in the string x000D              x000D           if   positiveSignIndex    -1   amp  amp   negativeSignIndex    -1     x000D               return result  x000D              x000D              handle postive sign x000D              x000D           if  positiveSignIndex    -1  x000D             x000D                 x000D                 make sure there is only one sign character x000D                 x000D              if   positiveSignIndex    val lastIndexOf         x000D               return result       x000D                  x000D                  make sure the sign is at the head or tail x000D                  x000D               if   positiveSignIndex  gt  0   amp  amp   positiveSignIndex  lt  nTailIndex      x000D                   return result  x000D                  x000D                  remove sign from string x000D                  x000D               val   val replace         trim                     x000D                 x000D              x000D              handle negative sign x000D              x000D           if  negativeSignIndex    -1  x000D             x000D                 x000D                 make sure there is only one sign character x000D                 x000D              if   negativeSignIndex    val lastIndexOf  -      x000D               return result       x000D                  x000D                  make sure the sign is at the head or tail x000D                  x000D               if   negativeSignIndex  gt  0   amp  amp   negativeSignIndex  lt  nTailIndex      x000D                   return result  x000D                  x000D                  remove sign from string x000D                  x000D               val   val replace  -      trim      x000D               sign   -1                   x000D                            x000D              x000D              make sure text length is greater than 0 x000D                     x000D           if val length    0   x000D              return result                               x000D             x000D           x000D           convert string to a number x000D           x000D        var r      lt any gt val   x000D        if   r    null   amp  amp    isNaN r     x000D                    x000D           result   r sign           x000D          x000D        return result       x000D       x000D   x000D   x000D

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Expounding on what Ryan said  TypeScript embraces the JavaScript idioms in general   var n     1      the unary   converts to number var b      2      the    converts truthy to true  and falsy to false var s      3     the     converts to string via toString     All the interesting in-depth details at JavaScript Type Conversion

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if you are talking about just types  as other people said  parseInt   etc will return the correct type  Also  if for any reason the value could be both a number or a string and you don t want to call parseInt    typeof expressions will also cast to the correct type   function f value number string     if typeof value    number          value   number    else         value   string

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Easiest way is to use  strVal or Number strVal   Examples   let strVal1    123 5  let strVal2    One  let val1a    strVal1 let val1b   Number strVal1  let val1c   parseFloat strVal1  let val1d   parseInt strVal1  let val1e    strVal1 - parseInt strVal1  let val2a    strVal2  console log  val1a- gt    val1a     123 5 console log  val1b- gt    val1b     123 5 console log  val1c- gt    val1c     123 5 console log  val1d- gt    val1d     123 console log  val1e- gt    val1e     0 5 console log  val2a- gt    val2a     NaN

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The Typescript way to do this would be   Number  1234      1234 Number  9BX9      NaN   as answered here  https   stackoverflow com a 23440948 2083492

[typescript] How to convert a string to number in TypeScript?

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