How to force JS to do math instead of putting two strings together

Question

I need javascript to add 5 to an integer variable  but instead it treats the variable as a string  so it write out the variable  then add 5 onto the end of the  string   How can I force it to do math instead   var dots   document getElementById  txt   value     5 function increase        dots   dots   5      Output  55  How can I force it to output 10

User · Accepted Answer

You have the line   dots   document getElementById  txt   value    in your file  this will set dots to be a string because the contents of txt is not restricted to a number   to convert it to an int change the line to   dots   parseInt document getElementById  txt   value  10     Note  The 10 here specifies decimal  base-10   Without this some browsers may not interpret the string correctly  See MDN  parseInt

User · Answer

I m adding this answer because I don t see it here   One way is to put a     character in front of the value  example   var x     11 5      3 5    x     15  I have found this to be the simplest way  In this case  the line   dots   document getElementById  txt   value    could be changed to   dots     document getElementById  txt   value     to force it to a number  NOTE            0         0   5      5    5       5

User · Answer

This also works for you    dots -  -5

User · Answer

UPDATED since this was last downvoted      I only saw the portion   var dots   5 function increase        dots   dots 5      before  but it was later shown to me that the txt box feeds the variable dots   Because of this  you will need to be sure to  cleanse  the input  to be sure it only has integers  and not malicious code   One easy way to do this is to parse the textbox with an onkeyup   event to ensure it has numeric characters    lt input size  40  id  txt  value  Write a character here   onkeyup  GetChar  event     gt    where the event would give an error and clear the last character if the value is not a number    lt script type  text javascript  gt      function GetChar  event           var keyCode     which  in event    event which   event keyCode          var yourChar   String fromCharCode            if  yourChar     0   amp  amp              yourChar     1   amp  amp              yourChar     2   amp  amp              yourChar     3   amp  amp               yourChar     4   amp  amp              yourChar     5   amp  amp              yourChar     6   amp  amp               yourChar     7   amp  amp              yourChar     8   amp  amp               yourChar     9                         alert   The character was not a number                var source   event target    event srcElement              source value   source value substring 0 source value-2                    lt  script gt    Obviously you could do that with regex  too  but I took the lazy way out   Since then you would know that only numbers could be in the box  you should be able to just use eval     dots   eval dots    5

User · Answer

You can add   behind the variable and it will force it to be an integer  var dots   5     function increase            dots    dots   5

User · Answer

DON T FORGET - Use parseFloat    if your dealing with decimals

User · Answer

After trying most of the answers here without success for my particular case  I came up with this   dots   - -dots - 5     The   signs are what confuse js  and this eliminates them entirely  Simple to implement  if potentially confusing to understand

User · Answer

the simplest   dots   dots 1 5    the dots will be converted to number

User · Answer

Number   dots   document getElementById  quot txt quot   value  dots   Number dots    5       from MDN Number  123          123 Number  123       123     true Number  12 3         12 3 Number  12 00        12 Number  123e-1       12 3 Number               0 Number null          0 Number  0x11         17 Number  0b11         3 Number  0o11         9 Number  foo          NaN Number  100a         NaN Number  -Infinity     -Infinity

User · Answer

parseInt   should do the trick  var number    25   var sum   parseInt number  10    10  var pin   number   10    Gives you  sum    35 pin     2510    http   www w3schools com jsref jsref parseint asp  Note  The 10 in parseInt number  10  specifies decimal  base-10   Without this some browsers may not interpret the string correctly  See MDN  parseInt

User · Answer

its really simple just  var total    1   yourFirstVariablehere     1   yourSecondVariablehere    this forces javascript to multiply because there is no confusion for   sign in javascript

[javascript] How to force JS to do math instead of putting two strings together

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