How to add two strings as if they were numbers

Question

I have two strings which contain only numbers   var num1    20       num2    30 5     I would have expected that I could add them together  but they are being concatenated instead   num1   num2        2030 5    How can I force these strings to be treated as numbers

User · Answer

If you want to perform operation with numbers as strings  as in the case where numbers are bigger than 64bits can hold  you can use the big-integer library   const bigInt   require  big-integer   bigInt  999   add  1   toString      output   1000

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convert the strings to floats with parseFloat string  or to integers with parseInt string

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I ve always just subtracted zero   num1-0   num2-0    Granted that the unary operator method is one less character  but not everyone knows what a unary operator is or how to google to find out when they don t know what it s called

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MDN docs for parseInt  MDN docs for parseFloat  In parseInt radix is specified as ten so that we are in base 10  In nonstrict javascript a number prepended with 0 is treated as octal  This would obviously cause problems   parseInt num1  10    parseInt num2  10    base10 parseFloat num1    parseFloat num2    Also see ChaosPandion s answer for a useful shortcut using a unary operator  I have set up a fiddle to show the different behaviors   http   jsfiddle net EtX6G   var ten    10   var zero ten    010   var one    1   var body   document getElementsByTagName  body   0    Append parseInt ten    parseInt one    Append parseInt zero ten    parseInt one    Append  ten    one   Append  zero ten    one    function Append text        body appendChild document createTextNode text        body appendChild document createElement  br

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Use the parseFloat method to parse the strings into floating point numbers   parseFloat num1    parseFloat num2

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var result   Number num1    Number num2

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I would recommend to use the unary plus operator  to force an eventual string to be treated as number  inside parenthesis to make the code more readable like the following     varname    So  in your case it s   var num1    20       num2    30 5    var sum     num1      num2       Just to test it console log  sum       50 5

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You can use parseInt to parse a string to a number  To be on the safe side of things  always pass 10 as the second argument to parse in base 10   num1   parseInt num1  10   num2   parseInt num2  10   alert num1   num2

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try  var x   parseFloat num1    parseFloat num2      or  depending on your needs   var x   parseInt num1    parseInt num2      http   www javascripter net faq convert2 htm  You might want to pick up the book Javascript  The Good Parts  by Douglas Crockford  Javascript has a rather sizeable colleciton of gotchas  This book goes a long way towards clarifying them  See also   http   www crockford com  http   javascript crockford com    and Mr  Crockford s excellent essay  Javascript  The World s Most Misunderstood Programming Language

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function sum        var x y z      x   Number document getElementById  input1   value       y   Number document getElementById  input2   value       z   x   y      document getElementById  result   innerHTML   z

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You can use this to add numbers   var x    num1    num2

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document getElementById currentInputChoosen  value -   -100    Works in my case  if you run into the same problem like me and can t find a solution for that case and find this SO question   Sorry for little bit off-topic  but as i just found out that this works  i thought it might be worth sharing   Don t know if it is a dirty workaround  or actually legit

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Make sure that you round your final answer to less than 16 decimal places for floats as java script is buggy   For example 5 - 7 6   -2 5999999999999996

User · Answer

Here  you have two options to do this  -     1 You can use the unary plus to convert string number into integer       2 You can also achieve this via parsing the number into corresponding type  i e parseInt    parseFloat   etc      Now I am going to show you here with the help of examples Find the sum of two numbers    Using unary plus operator   lt  DOCTYPE html gt   lt html gt   lt body gt    lt H1 gt Program for sum of two numbers  lt  H1 gt   lt p id  myId  gt  lt  p gt   lt script gt  var x   prompt  Please enter the first number      prompt will always return string value var y   prompt  Please enter the second nubmer     var z    x    y      document getElementById  myId   innerHTML   Sum of   x   and   y   is   z   lt  script gt   lt  body gt   lt  html gt    Using parsing approach-   lt  DOCTYPE html gt   lt html gt   lt body gt    lt H1 gt Program for sum of two numbers  lt  H1 gt   lt p id  myId  gt  lt  p gt   lt script gt  var x   prompt  Please enter the first number     var y   prompt  Please enter the second number        var z   parseInt x    parseInt y   document getElementById  myId   innerHTML   Sum of   x   and   y   is   z   lt  script gt   lt  body gt   lt  html gt

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I use this in my project I use   sign to treat string as a number  in with interesst variable    lt script gt  function computeLoan    var amount   document getElementById  amount   value  var interest rate   document getElementById  interest rate   value  var days   document getElementById  days   value  var interest    amount    interest rate    01     days  var payment     amount   days    interest  toFixed 2   var with interest    amount    interest rate    01    var with interesst     amount    interest rate    01       amount   payment   payment toString   replace   B     d 3       d   g        document getElementById  payment   innerHTML    Target Daily   PHP  payment  document getElementById  with interesst   innerHTML    Amount w Interest     PHP  with interesst     lt  script gt    lt div name  printchatbox  id  printchatbox  gt    lt form id  Calculate  class  form-horizontal  gt      lt h2 gt You Can Use This Calculator Before Submit  lt  h2 gt      lt p gt Loan Amount  PHP lt input id  amount  type  number  min  1  max  1000000   onchange  computeLoan    gt  lt  p gt      lt p gt Interest Rate   lt input id  interest rate  type  number  min  0  max  100  value  10  step   1  onchange  computeLoan    gt   lt  p gt       lt p gt Term lt select id  days  type  number  min  1  max  72  step   1  onchange  computeLoan    gt       lt option value  40  gt 40 Days lt  option gt       lt option value  50  gt 50 Days lt  option gt       lt option value  60  gt 60 Days lt  option gt       lt option value  70  gt 70 Days lt  option gt       lt option value  80  gt 80 Days lt  option gt       lt option value  90  gt 90 Days lt  option gt       lt option value  100  gt 100 Days lt  option gt       lt option value  120  gt 120 Days lt  option gt       lt  select gt       lt  p gt                              lt h2 id  payment  gt  lt  h2 gt      lt h2 id   with interesst  gt  lt  h2 gt    lt  form gt   lt  div gt    Hope it helps

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cr05s19xx suggested on a duplicate question   JavaScript is a bit funny when it comes to numbers and addition   Giving the following   20  -  30    10     returns 10 as a number  20     30     2030      Returns them as a string The values returned from document getElementById are strings  so it s better to parse them all  even the one that works  to number  before proceeding with the addition or subtraction  Your code can be   function myFunction       var per   parseInt document getElementById  input1   value     var num   parseInt document getElementById  input2   value     var sum    num   100    per    var output   num - sum     console log output      document getElementById  demo   innerHTML   output     function myFunction2       var per   parseInt document getElementById  input3   value     var num   parseInt document getElementById  input4   value     var sum    num   100    per    var output   sum   num     console log output      document getElementById  demo1   innerHTML   output

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Try this if you are looking for simple Javascript code and want to use two input box and add numbers from the two value  Here s the code       Enter the first number   lt input type  text  id  num1    gt  lt br   gt      Enter the seccond number   lt input type  text  id  num2    gt  lt br   gt       lt input type  button  onclick  call    value  Add   gt        lt script type  text javascript  gt      function call        var q parseInt document getElementById  num1   value       var w parseInt document getElementById  num2   value       var result q w             lt  script gt    for more details please visit http   informativejavascript blogspot nl 2012 12 javascript-basics html

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I would use the unary plus operator to convert them to numbers first       num1    num2

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You may use like this   var num1    20       num2    30 5    alert  num1 1     num2 1      result 50 5   When apply  1 in num1  convert string a number   if num1 contains a letter or a comma  returns NaN multiplying by 1   if num1 is null  num1 returns 0  kind regards

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If you need to add two strings together which are very large numbers you ll need to evaluate the addition at every string position   function addStrings str1  str2     str1a   str1 split     reverse      str2a   str2 split     reverse      let output         let longer   Math max str1 length  str2 length     let carry   false    for  let i   0  i  lt  longer  i          let result     if  str1a i   amp  amp  str2a i           result   parseInt str1a i     parseInt str2a i           else if  str1a i   amp  amp   str2a i           result   parseInt str1a i           else if   str1a i   amp  amp  str2a i           result   parseInt str2a i               if  carry            result    1          carry   false            if result  gt   10          carry   true        output    result toString   1        else         output    result toString                output   output split     reverse   join         if carry        output    1    output        return output

[javascript] How to add two strings as if they were numbers?

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