一段javascript代碼的解釋

Question

我是 javascript 的初學者，我正在查看以下代碼。

  var type_select = '<select id="type_select" style="margin-bottom:0px;">';
  var i;
  var customer_group = <?php echo json_encode($customer_group);?>;
  for (i = 0; i < customer_group.length; ++i) {
      //console.log(customer_group[i].group_id);
      if (customer_group[i].group_name == table_column_1){
          type_select = type_select+'<option value='+customer_group[i].group_id+' selected>'+customer_group[i].group_name+'</option>';
      }else{
          type_select = type_select+'<option value='+customer_group[i].group_id+'>'+customer_group[i].group_name+'</option>';
      }
  }
  type_select = type_select+'</select>';
  //not allow to click header
  if ( col == 0 ) {
      return;
  }

請幫助我了解它可能在做什么。 也許有方向。 我不確定這段代碼是否足夠，請盡力幫助我並盡可能多地向我解釋。 您的幫助將不勝感激。

Answer 1

它正在構建一個帶有一些選項的選擇下拉框

<select id="type_select" style="margin-bottom:0px;">
    <option value="some-value">Some text</option>
    <option value="some-other-value">Some other text</option>
    <option value="yet-another-value" selected>More text this one is selected on load</option>
</select>

查看您發布的代碼片段，然后它完全沒有任何作用

希望有幫助

Answer 2

var type_select = '<select id="type_select" style="margin-bottom:0px;">';
var i;

// this part of code will be interpreted by PHP Engine, on client side you will find an JSON representation of
// "Customer_group", probably gotten from database, or file
var customer_group = <?php echo json_encode($customer_group);?>;

for (i = 0; i < customer_group.length; ++i) {
    // here, you are building a HTML string, this will be attached to DOM using
    // ex : document.getElementById('YOUR_DOM_ID').innerHTML = type_select;
    if (customer_group[i].group_name == table_column_1){
        type_select = type_select+'<option value='+customer_group[i].group_id+' selected>'+customer_group[i].group_name+'</option>';
    }else{
        type_select = type_select+'<option value='+customer_group[i].group_id+'>'+customer_group[i].group_name+'</option>';
    }
}
type_select = type_select+'</select>';
//not allow to click header
if ( col == 0 ) {
    return;
}