html select动态赋值

var positionIds = $("savePerformanceWorkflowExamineResearch_performanceWorkflowExamine_positionId");
    positionIds.options.length = 1;
    positionIds.options[0].selected = "selected";
    DWREngine.setAsync(false);
    performancePositionService.getPositionsByUserId(employeeId, function(positions) {
    if (positions != undefined && positions != null && positions.length > 0) {
    for (var i = 0; i < positions.length; i++) {
    positionIds.options[positionIds.options.length] = new Option(positions[i].positionName, positions[i].id);
    }
    }
    });