Uncaught TypeError Cannot read property value of undefined

Question

I have some JavaScript code that gives this error  Uncaught TypeError  Cannot read property  value  of undefined   Code  var i1   document getElementById  i1    var i2   document getElementById  i2    var   i     user    document getElementsByName  username   0    pass    document getElementsByName  password   0     if     i user value length  gt   1     i1 value         else   i1 value    Acc      if     i pass value length  gt   1     i2 value         else   i2 value    Pwd       What does this error mean

User · Answer

Either document getElementById  i1    document getElementById  i2    or document getElementsByName  username   0  is returning no element  Check  that all elements exist

User · Answer

First  you should make sure that document getElementsByName  username   0  actually returns an object and not  undefined   You can simply check like   if  typeof document getElementsByName  username   0      undefined     Similarly for the other element password

User · Answer

Try this  It always works  and you will get NO TypeError   try       var i1   document getElementById  i1        var i2   document getElementById  i2        var   i     user    document getElementsByName  username   0    pass    document getElementsByName  password   0         if     i user value length  gt   1     i1 value         else   i1 value    Acc         if     i pass value length  gt   1     i2 value         else   i2 value    Pwd       catch e       if e          If fails  Do something else

User · Answer

You can just create a function to check if the variable exists  else will return a default value    function isSet element  defaultVal        if typeof element     undefined             return element              console log  one missing element         return defaultVal      And use it in a variable check   var variable   isSet variable   Default value

User · Answer

The posts here help me a lot on my way to find a solution for the Uncaught TypeError  Cannot read property  value  of undefined issue   There are already here many answers which are correct  but what we don t have here is the combination for 2 answers that i think resolve this issue completely   function myFunction field  data     if  typeof document getElementsByName   field    0      undefined      document getElementsByName   field    0  value data         The difference is that you make a check if a property is defined or not  and if the check is true then you can try to assign it a value

User · Answer

You code looks like automatically generated from other code - you should check that html elements with id i1 and i2 and name username and password exists before processing them

User · Answer

Seems like one of your values  with a property key of  value  is undefined  Test that i1  i2and   i are defined before executing the if statements   var i1   document getElementById  i1    var i2   document getElementById  i2    var   i     user    document getElementsByName  username   0    pass    document getElementsByName  password   0     if i1  amp  amp  i2  amp  amp    i user  amp  amp    i pass        if     i user value length  gt   1     i1 value         else   i1 value    Acc          if     i pass value length  gt   1     i2 value         else   i2 value    Pwd

[javascript] Uncaught TypeError: Cannot read property 'value' of undefined

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