How to create a function for Onkeyup

I am trying to write a function to analyze the users input before calling Onkeyup. I am not sure where to write this if statement, or if I have the correct syntax. I wrote the if statement inside the asset-tag class. This is my code:

const getAssetInfo = (assetTag, index) => {
    // get the table row that this input is in
    $.get("http://localhost:3000/assets/" + assetTag , (data) => {
      // find the `.description` element and set it's value 
      if (data){
        $(`#manufacturer_serial_no${index}`).val(data.serial_no);
        $(`#description${index}`).val(data.description);
        $(`#cost${index}`).val(data.cost);
        $(`#po_no${index}`).val(data.po_no);
      }
      
      console.log(data);

    })
    
    .fail(() => {
        // alert("DONE");
        // console.log(index);
        $(`#manufacturer_serial_no${index}`).val("");
        $(`#description${index}`).val("");
        $(`#cost${index}`).val("");
        $(`#po_no${index}`).val("");
    });

};

$('document').ready(() => {
    

    // Handler to Add New Asset
    const table = $("#formTable tbody");
    let count = 1;

    $('#add').click(() => {
        
        const newRow = `
        
                        
                    <tr index="${count}">
                    <form>
                    <td><input 
                    class="asset-tag" id='asset_tag_no${count}' type='text' 
                    if (input.length >= 4){
                        console.log('not enough characters to call API endpoint');
                    }
                    else{
                    onkeyup = "getAssetInfo(this.value,${count})";
                    }
                    bottom required /></td> 
                    
                    <td><input  class="serial-no" id='manufacturer_serial_no${count}' type='text' bottom required readonly/></td>
                    <td><textarea class="description" id='description${count}' type='text' bottom required readonly description></textarea></td>
                    <td><input id='cost${count}' type='value' bottom require readonly/></td>
                    <td><input id='po_no${count}' type='text' bottom require readonly/></td>
                    <td><textarea id='remarks${count}' type='text' bottom remarks></textarea></td>
                    <td><button type="button" index="${count}" class="btn btn-danger btn-remove">X</button></td>
                    </form>
                </tr>
        `;

        table.append(newRow);
        // Handler to Remove New Asset
        $('.btn-remove').click(function(){
            let index = $(this).attr('index');
            $(`tr[index='${index}'`).remove();
        });

        count++;
    });

I want this error in the console log to only execute when a certain amount of characters are in the box instead of each time a character is inputted.