JavaScript Parsing a string Boolean value

Question

JavaScript has parseInt   and parseFloat    but there s no parseBool or parseBoolean method in the global scope  as far as I m aware   I need a method that takes strings with values like  true  or  false  and returns a JavaScript Boolean   Here s my implementation   function parseBool value        return  typeof value      undefined                 false                  trim using jQuery trim   s source             value replace    s   s   g      toLowerCase        true       Is this a good function  Please give me your feedback   Thanks

User · Answer

I shamelessly converted Apache Common s toBoolean to JavaScript   JSFiddle  https   jsfiddle net m2efvxLm 1   Code    x000D   x000D  function toBoolean str    x000D    if  str     true     x000D      return true  x000D      x000D    if   str    x000D      return false  x000D      x000D    switch  str length    x000D      case 1    x000D        var ch0   str charAt 0   x000D        if  ch0     y     ch0     Y     x000D            ch0     t     ch0     T     x000D            ch0     1     x000D          return true  x000D          x000D        if  ch0     n     ch0     N     x000D            ch0     f     ch0     F     x000D            ch0     0     x000D          return false  x000D          x000D        break  x000D        x000D      case 2    x000D        var ch0   str charAt 0   x000D        var ch1   str charAt 1   x000D        if   ch0     o     ch0     O    amp  amp  x000D             ch1     n     ch1     N       x000D          return true  x000D          x000D        if   ch0     n     ch0     N    amp  amp  x000D             ch1     o     ch1     O       x000D          return false  x000D          x000D        break  x000D        x000D      case 3    x000D        var ch0   str charAt 0   x000D        var ch1   str charAt 1   x000D        var ch2   str charAt 2   x000D        if   ch0     y     ch0     Y    amp  amp  x000D             ch1     e     ch1     E    amp  amp  x000D             ch2     s     ch2     S       x000D          return true  x000D          x000D        if   ch0     o     ch0     O    amp  amp  x000D             ch1     f     ch1     F    amp  amp  x000D             ch2     f     ch2     F       x000D          return false  x000D          x000D        break  x000D        x000D      case 4    x000D        var ch0   str charAt 0   x000D        var ch1   str charAt 1   x000D        var ch2   str charAt 2   x000D        var ch3   str charAt 3   x000D        if   ch0     t     ch0     T    amp  amp  x000D             ch1     r     ch1     R    amp  amp  x000D             ch2     u     ch2     U    amp  amp  x000D             ch3     e     ch3     E       x000D          return true  x000D          x000D        break  x000D        x000D      case 5    x000D        var ch0   str charAt 0   x000D        var ch1   str charAt 1   x000D        var ch2   str charAt 2   x000D        var ch3   str charAt 3   x000D        var ch4   str charAt 4   x000D        if   ch0     f     ch0     F    amp  amp  x000D             ch1     a     ch1     A    amp  amp  x000D             ch2     l     ch2     L    amp  amp  x000D             ch3     s     ch3     S    amp  amp  x000D             ch4     e     ch4     E       x000D          return false  x000D          x000D        break  x000D        x000D      default  x000D        break  x000D      x000D   x000D    return false  x000D    x000D  console log toBoolean  yEs        true x000D  console log toBoolean  yES        true x000D  console log toBoolean  no        false x000D  console log toBoolean  NO        false x000D  console log toBoolean  on        true x000D  console log toBoolean  oFf        false x000D  Inspect this element  and view the console output  x000D   x000D   x000D

User · Answer

It depends how you wish the function to work   If all you wish to do is test for the word  true  inside the string  and define any string  or nonstring  that doesn t have it as false  the easiest way is probably this   function parseBoolean str      return  true i test str       If you wish to assure that the entire string is the word true you could do this   function parseBoolean str      return   true  i test str

User · Answer

Why not keep it simple   var parseBool   function str        if  typeof str      string   amp  amp  str toLowerCase       true               return true       return  parseInt str   gt  0

User · Answer

Personally I think it s not good  that your function  hides  invalid values as false and - depending on your use cases - doesn t return true for  1    Another problem could be that it barfs on anything that s not a string   I would use something like this   function parseBool value      if  typeof value      string          value   value replace    s   s   g      toLowerCase         if  value      true     value      false          return value      true         return     returns undefined     And depending on the use cases extend it to distinguish between  0  and  1     Maybe there is a way to compare only once against  true   but I couldn t think of something right now

User · Answer

You can add this code   function parseBool str       if  str length    null        return str    1   true   false      else       return str     true    true   false           Works like this   parseBool 1    true parseBool 0    false parseBool  true     true parseBool  false     false

User · Answer

You can use JSON parse for that   JSON parse  true      returns boolean true

User · Answer

I like the solution provided by RoToRa  try to parse given value  if it has any boolean meaning  otherwise - don t   Nevertheless I d like to provide small modification  to have it working more or less like Boolean TryParse in C   which supports out params  In JavaScript it can be implemented in the following manner   var BoolHelpers         tryParse  function  value            if  typeof value     boolean     value instanceof Boolean              return value          if  typeof value     string     value instanceof String                value   value trim   toLowerCase                if  value      true     value      false                   return value      true                     return   error  true  msg   Parsing error  Given value has no boolean meaning               The usage   var result   BoolHelpers tryParse  false    if  result error  alert result msg

User · Answer

last but not least  a simple and efficient way to do it with a default value    ES5  function parseBool value  defaultValue        return  value     true     value     false     value     true    value     false   amp  amp  JSON parse value     defaultValue      ES6   a shorter one liner  const parseBool    value  defaultValue    gt    true    false   true  false  includes value   amp  amp  JSON parse value     defaultValue   JSON parse is efficient to parse booleans

User · Answer

You can use JSON parse or jQuery parseJSON and see if it returns true using something like this   function test  input        try           return     parseJSON input toLowerCase           catch  e

User · Answer

Enough to using eval javascript function to convert string to boolean    eval  true     eval  false

User · Answer

stringjs has a toBoolean   method   http   stringjs com  methods toboolean-tobool  S  true   toBoolean     true S  false   toBoolean     false S  hello   toBoolean     false S true  toBoolean     true S  on   toBoolean     true S  yes   toBoolean     true S  TRUE   toBoolean     true S  TrUe   toBoolean     true S  YES   toBoolean     true S  ON   toBoolean     true S     toBoolean     false S undefined  toBoolean     false S  undefined   toBoolean     false S null  toBoolean     false S false  toBoolean     false S     toBoolean     false S 1  toBoolean     true S -1  toBoolean     false S 0  toBoolean     false

User · Answer

You can try the following   function parseBool val        if   typeof val      string   amp  amp   val toLowerCase        true     val toLowerCase        yes       val     1          return true      else if   typeof val      string   amp  amp   val toLowerCase        false     val toLowerCase        no       val     0          return false       return null      If it s a valid value  it returns the equivalent bool value otherwise it returns null

User · Answer

I would be inclined to do a one liner with a ternary if   var bool value   value     true    true   false   Edit  Even quicker would be to simply avoid using the a logical statement and instead just use the expression itself   var bool value   value     true     This works because value     true  is evaluated based on whether the value variable is a string of  true   If it is  that whole expression becomes true and if not  it becomes false  then that result gets assigned to bool value after evaluation

User · Answer

Wood-eye be careful   After looking at all this code  I feel obligated to post   Let s start with the shortest  but very strict way   var str    true   var mybool   JSON parse str     And end with a proper  more tolerant way   var parseBool   function str            console log typeof str          strict  JSON parse str       if str    null          return false       if  typeof str      boolean                 if str     true              return true           return false              if typeof str      string                 if str                    return false           str   str replace    s   s   g               if str toLowerCase       true     str toLowerCase       yes               return true           str   str replace    g                str   str replace    s  - s  g   -                  var isNum   string match    0-9         null         var isNum      d    test str       if  isNaN str           return  parseFloat str     0        return false      Testing   var array 1   new Array true  1   1  -1   -1     - 1    true    TrUe      true        TrUe   1 0   1 5    1 5   1 5  5  -3  -0 1  0 1    - 0 1   Infinity   Infinity   -Infinity   -Infinity    - Infinity     yEs     var array 2   new Array null      false   false       false        f alse    FaLsE   0   00    1 0   0 0   0 0    0 0    100a    1 00     0    0 0   0 0   -0 0   -0 0     -1a     abc      for var i  0  i  lt  array 1 length   i   console log  array 1   i       array 1 i          parseBool array 1 i       for var i  0  i  lt  array 2 length   i   console log  array 2   i       array 2 i          parseBool array 2 i       for var i  0  i  lt  array 1 length   i   console log parseBool array 1 i      for var i  0  i  lt  array 2 length   i   console log parseBool array 2 i

[javascript] JavaScript: Parsing a string Boolean value?

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