JSFiddle - React, Tailwind, and code Playground

HTML

<select id="options">
  <option value="">Choose...</option>
  <option value="3134" >Tight Buffered </option>
  <option value="3135" >Loose Tube 900um </option>
  <option value="3154" >Loose Tube 2mm </option>
  <option value="3136" >Break-Out 2mm </option>
  <option value="3138" >Micro Cable 2mm </option>
  <option value="3139" >Nano Cable 900um </option>
  <option value="3183" >Steel Tape Armoured 900um </option>
</select>
<select id="options2">
  <option value="">Choose...</option>
  <option value="3111">LC </option>
  <option value="3110">LC/A </option>
  <option value="3112">E2000 </option>
  <option value="3113">E2/A </option>
  <option value="3114">FC </option>
  <option value="3115">FC/A </option>
  <option value="3116">ST </option>
  <option value="3117">SC </option>
  <option value="3118">SC/A </option>
</select>
<select id="options3">
  <option value="">Choose...</option>
  <option value="3175">2 </option>
  <option value="3121">4 </option>
  <option value="3122">6 </option>
  <option value="3123">8 </option>
  <option value="3124">12 </option>
  <option value="3125">16 </option>
  <option value="3126">24 </option>
  <option value="3176">48 </option>
</select>
<select id="options4">
  <option value="">Choose...</option>
  <option value="3127">OS1/2 </option>
  <option value="3182">G657A1 </option>
  <option value="3128">OM1 </option>
  <option value="3129">OM2 </option>
  <option value="3130">OM3</option>
  <option value="3131">OM4 </option>
</select>
<select id="options5">
  <option value="">Choose...</option>
  <option value="3142">LC </option>
  <option value="3143">LC/A </option>
  <option value="3144">E2000 </option>
  <option value="3145">E2/A </option>
  <option value="3146">FC </option>
  <option value="3147">FC/A </option>
  <option value="3148">ST </option>
  <option value="3149">SC </option>
  <option value="3150">SC/A </option>
</select>
<select id="options6">
  <option value="">Choose...</option>
  <option value="3151">LZSH </option>
 ...

JavaScript

var sku1 = sku2 = sku3 = sku4 = sku5 = sku6 = length = '';
$("#options").change(function(){

    switch($(this).val()){
        case "":
             sku1 = '';
        break;
            
        case "3134":
             sku1 = 'TB';
        break;
        case "3135":
             sku1 = 'LT';
        break;
        case "3154":
            sku1 = 'LTR';
        break;
        case "3136":
             sku1 = 'BO';
        break;
        case "3138":
             sku1 = 'MC';
        break;
        case "3139":
             sku1 = 'NC';
        break;
        case "3183":
              sku1 = 'STA';
        break;
    }
    $('#sku').val(sku1+sku2+sku3+sku4+sku5+sku6+length);
});
$("#options2").change(function(){
    switch($(this).val()){
        case "3111":
              sku2 = 'LC';
        break;
        case "3110":
             sku2 ='LCA';
        break;
        case "3112":
             sku2 ='E2000';
        break;
        case "3113":
             sku2 ='E2A';
        break;
        case "3114":
             sku2 ='FC';
        break;
        case "3115":
             sku2 ='FCA';
        break;
        case "3116":
             sku2 ='ST';
        break;
        case "3117":
             sku2 ='SC';
        break;
        case "3118":
             sku2 ='SCA';
        break;
    }
    $('#sku').val(sku1+sku2+sku3+sku4+sku5+sku6+length);
});
$("#options3").change(function(){
    switch($(this).val()){
        case "3175":
              sku3 = '2';
        break;
        case "3121":
             sku3 ='4';
        break;
        case "3122":
             sku3 ='6';
        break;
        case "3123":
             sku3 ='8';
        break;
        case "3124":
             sku3 ='12';
        break;
        case "3125":
             sku3 ='16';
        break;
        case "3126":
             sku3 ='24';
        break;
        case "3176":
             sku3 ='48';
        break;
    }
   ...