passing value from a function to a form attribute in javascript

Question

Got a form field that's being checked by a function if value is numeric or not. After the returning the check, I need another function that is meant to pass an attribute value to the field.

Example:

FunctionA checks if value is numeric or not
FunctionB get a specific digit from FunctionA which is set as the attribute of the form field
If form field value is numeric, set the maxlength to 20
Else if it's not numeric, set the maxlength to 10

HTML:

<form method="post"  action="">

<input type="text" name="txt" onblur="numChk(this.value);" maxlength="getMax();" />

<p id="fmsg"></p>

<input type="submit" name="sub" />

</form>

Javascript:

<script type="text/javascript">
function numChk (num){
 //var num = num;
    if(!isNaN(num)){
          document.getElementById("fmsg").innerHTML = '<strong>' + num + ' is a number </strong>';
          getMax(maxVal) = 14;
    } else{
          document.getElementById("fmsg").innerHTML = '<em>' + num + ' is not a number </em>';
          getMax(maxVal) = 11;
    }

}

function getMax(maxVal){
    return maxVal;
}
</script>

Hope to get some help with this.

What are you trying to do? This sounds like an XY-problem: http://meta.stackexchange.com/questions/66377/what-is-the-xy-problem — Halcyon, Sep 06 '13 at 15:57
Thanks @FritsvanCampen - I have been looking for that expression for ages! — mplungjan, Sep 06 '13 at 16:01

score 0 · Answer 1 · answered Sep 06 '13 at 16:03

I would try doing this...

Just call the function in your HTML without a parameter and add an ID:

<input type="text" name="txt" id="txt" onblur="numChk();" maxlength="getMax();" />

Then in your function, get the value of the input field:

function numChk (){
     //var num = num;
     var num = parseInt(document.getElementById("txt").value); //Get input field value

     if(!isNaN(num)){
         document.getElementById("fmsg").innerHTML = '<strong>' + num + ' is a number </strong>';
         getMax(maxVal) = 14;
     }else{
         document.getElementById("fmsg").innerHTML = '<em>' + num + ' is not a number </em>';
         getMax(maxVal) = 11;

     }

}

score 0 · Accepted Answer · edited May 23 '17 at 12:11

Demo: http://jsfiddle.net/Q7A32/

function isNumber(n) {
  return !isNaN(parseFloat(n)) && isFinite(n);
}

var inp = document.getElementById('myinput'),
    output = document.getElementById("fmsg");

inp.onkeyup = function() {
    var val = this.value;
    if(isNumber(val)){
        output.innerHTML = '<strong>' + val + ' is a number </strong>';
        this.maxLength = 14;
    }else{
        output.innerHTML = '<em>' + val + ' is not a number </em>';
        this.maxLength = 11;
    }
};

Note: To check if the string is numerical I use https://stackoverflow.com/a/1830844/1529630

passing value from a function to a form attribute in javascript

2 Answers2