Form input check Javascript

Question

I have an html form and want to create a Javascript code that would check if the Tel. field include only numbers. It is an exercise so I don't want to use jQuery or any other library. I put together this:

HTML

<form action="" method="post" enctype="multipart/form-data" name="form1" id="form1" onsubmit="return numberedFieldsCheck()">
<table>
<tr>
<td>
 <label for="tel">Telephone</label></td>
<td>
 <input type="text" placeholder="00441293603275" name="tel" id="tel" />
 <span id="telFieldIntCheck" style="display:none;color:red">You can only use numbers.</span>
</td>
<td>
 <input type="submit" name="button" id="button" value="Submit" />
 </td>
</tr>
</table></form>

JS

function numberedFieldsCheck(){
    var x=document.getElementById('tel').value;// retrieving value from the form
    console.log(x);
    if(!integerCheck(x)){
        alert('wrong format');
        document.getElementById('telFieldIntCheck').style.display="inline";
        return false;
        }
    }

function integerCheck(userInput) {
var userInputArr=userInput.split('');
for (i=0;i<userInputArr.length;i++){
    if (typeof userInputArr[i]=="number")
            {console.log('format ok')} 
    else {return false};
  }
}

Can you help me with the code? It alerts wrong format regardless of what I put into the input field. Console logs appear for a millisecond and disappear straight away.

Answer 1

Since you only need to check if the field contains only numbers, this should work :

function numberedFieldsCheck(){
    var x=document.getElementById('tel').value;

    // Checks if the field is empty.
    if(x.trim() == '') {
    alert("Tel field can't be empty.");
    return false;
    }

    if(!integerCheck(x)){
        alert('Wrong format !');
        document.getElementById('telFieldIntCheck').style.display="inline";
        return false;
    }

    alert("Alright !");
    // Note that this return true is important. You weren't 
    // returning anything even in the case where everything was fine. 
    // If you don't, it will return 'undefined' by default, which is 
    // casted to 'false' in checks. So that means the function returns
    // false even if everything is alright.
    return true;
}

function integerCheck(userInput) {

    // Now, all the elements of usrInputArr will contain strings only.
    // That means typeof <element> will always return "string".
    var userInputArr=userInput.split('');

    for (i=0;i<userInputArr.length;i++){
        char = userInputArr[i];
        // Comparing by ASCIIs should work just fine.
        if (! (char >= '0' && char <= '9' || char == ' ') )
            return false;
    }

    return true;
}

You should also do what @hindmost said in the comments of your question i.e. changing the forms onsubmit to return numberFieldCheck().