String Format not work in TypeScript

Question

String Format does not work in TypeScript  Error    The property  format  does not exist on value of type      prototype  String  fromCharCode    codes  number     string     value   any   string  new value   any   String           attributes  Title     String format      Settings labelKeyValuePhraseCollection   WAIT DAYS         originalAttributes Days

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I am using TypeScript version 3 6 and I can do like this   let templateStr    This is an  0  for  1  purpose    const finalStr   templateStr format  example    format       This is an example for format purpose

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String Interpolation  Note  As of TypeScript 1 4  string interpolation is available in TypeScript   var a    Hello   var b    World    var text      a    b     This will compile to   var a    Hello   var b    World   var text   a         b    String Format  The JavaScript String object doesn t have a format function  TypeScript doesn t add to the native objects  so it also doesn t have a String format function   For TypeScript  you need to extend the String interface and then you need to supply an implementation   interface String       format    replacements  string     string     if   String prototype format      String prototype format   function         var args   arguments      return this replace     d    g  function match  number           return typeof args number      undefined            args number            match                          You can then use the feature   var myStr    This is an  0  for  0  purposes   1     alert myStr format  example    end       You could also consider string interpolation  a feature of Template Strings   which is an ECMAScript 6 feature - although to use it for the String format use case  you would still need to wrap it in a function in order to supply a raw string containing the format and then positional arguments  It is more typically used inline with the variables that are being interpolated  so you d need to map using arguments to make it work for this use case   For example  format strings are normally defined to be used later    which doesn t work      Works var myFormatString    This is an  0  for  0  purposes   1        Compiler warnings  a and b not yet defines  var myTemplateString    This is an   a  for   a  purposes    b      So to use string interpolation  rather than a format string  you would need to use   function myTemplate a  string  b  string        var myTemplateString    This is an   a  for   a  purposes    b       alert myTemplate  example    end       The other common use case for format strings is that they are used as a resource that is shared  I haven t yet discovered a way to load a template string from a data source without using eval

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You can declare it yourself quite easily    interface StringConstructor       format   formatString  string     replacement  any      gt  string     String format           This is assuming that String format is defined elsewhere  e g  in Microsoft Ajax Toolkit   http   www asp net ajaxlibrary Reference String-format-Function ashx

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As a workaround which achieves the same purpose  you may use the sprintf-js library and types   I got it from another SO answer

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FIDDLE  https   jsfiddle net 1ytxfcwx   NPM  https   www npmjs com package typescript-string-operations  GITHUB  https   github com sevensc typescript-string-operations  I implemented a class for String  Its not perfect but it works for me   use it i e  like this   var getFullName   function salutation  lastname  firstname        return String Format   0   1 U   2 L    salutation  lastname  firstname     export class String       public static Empty  string            public static isNullOrWhiteSpace value  string   boolean           try               if  value    null    value     undefined                   return false               return value replace   s g      length  lt  1                    catch  e                return false                       public static Format value     args   string           try               return value replace     d          g  function  match  i                    var s   match split                       if  s length  gt  1                        i   i 0                       match   s 1  replace                                              var arg   String formatPattern match  args i                    return typeof arg     undefined   amp  amp  arg    null   arg   String Empty                                    catch  e                return String Empty                       private static formatPattern match  arg   string           switch  match                case  L                   arg   arg toLowerCase                    break              case  U                   arg   arg toUpperCase                    break              default                  break                     return arg            EDIT   I extended the class and created a repository on github  It would be great if you can help to improve it   https   github com sevensc typescript-string-operations  or download the npm package  https   www npmjs com package typescript-string-operations

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I solved it like this   1 Created a function  export function FormatString str  string     val  string        for  let index   0  index  lt  val length  index          str   str replace     index     val index          return str      2 Used it like the following   FormatString   0  is  1   2     This    formatting    hack

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If you are using NodeJS  you can use the build-in util function  import   as util from  quot util quot   util format  My string   s    foo     Document can be found here  https   nodejs org api util html util util format format args

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You can use TypeScript s native string interpolation in case if your only goal to eliminate ugly string concatenations and boring string conversions   var yourMessage    Your text   yourVariable  your text continued   yourExpression  and so on     NOTE    At the right side of the assignment statement the delimiters are neither single or double quotes  instead a special char called backtick or grave accent   The TypeScript compiler will translate your right side special literal to a string concatenation expression  With other words this syntax is not relies the ECMAScript 6 feature instead a native TypeScript feature  Your generated javascript code remains compatible

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