如何通过JavaScript选择选择标签的选项？

Question

Below javascript to populate years, now need to select year that is posted from frontend.

eg if year 1903 is sent the option with value 1903 should be selected.

var start = 1900;
var end = new Date().getFullYear();
var options = "";
var yearpost = "<?php echo $year ?>";
for (var year = start; year <= end; year++) {
  options += "<option "
  if (year == yearpost) {
    document.write('selected')
  }
  ">" + year + "</option>";
}
document.getElementById("year").innerHTML = options;

Answer 1

You wrongly wote document.write instead of options += inside if block :

 var start = 1900; var end = new Date().getFullYear(); var options = ""; var yearpost = "2011"; for (var year = start; year <= end; year++) { options += "<option "; if (year == parseInt(yearpost)) { options += ('selected') } options += ">" + year + "</option>"; } document.getElementById("year").innerHTML = options; 

 <select id="year"></select> 

Or you can simplify the if statement to this:
options += '<option ' + (year == parseInt(yearpost) ? ' selected' : '') + '>' + year + '</option>';

Answer 2

If I understood correctly you want the option to be selected when it matches the year. The way you're doing it you are writing to the document, instead you should add it to the string you're creating. Inside your if statement try doing this instead : option += "selected"