javascript - else 语句不执行 JavaScript

Question

嘿伙计们，无论条件是什么，每次执行 if 语句时都在下面的代码中。

function addRow(tableID) {

            var table = document.getElementById(tableID);
            if((document.getElementById('select_degree').style.visibility = 'hidden')&&(document.getElementById('select_degree')!=null)){
              document.getElementById('select_degree').style.visibility = 'visible';
              document.getElementById('select_ratings').style.visibility  = 'visible';
             }

            else{ 
            var rowCount = table.rows.length;
            var new_row = table.rows[rowCount-1];  


            var row = table.insertRow(rowCount);


            var colCount = table.rows[0].cells.length;




            for(var i=0; i<colCount; i++) {

                var newcell = row.insertCell(i);


                newcell.innerHTML = new_row.cells[i].innerHTML;
            }
           }             
        }

当 document.getelementById('add_ Degree') 为 null 时，出现错误:

document.getElementById("select_degree") is null
addRow(tableID="add_degree")

但是如果元素为 null，我已经有一个 else 语句

Answer 1

您的 if 语句未使用正确的运算符。将 = (用于赋值)替换为比较运算符:==。此外，在尝试检查元素的属性之前，必须检查该元素是否存在。如果不这样做，当元素不存在时，您将收到异常。

这是您的代码，已更正和清理:

function addRow(tableID) {
    var objSelectDegree = document.getElementById('select_degree');
    if (objSelectDegree != null && objSelectDegree.style.visibility == 'hidden') {
        objSelectDegree.style.visibility = 'visible';
        document.getElementById('select_ratings').style.visibility = 'visible';
    }
    else {
        // Moved table var to else block - it was not used unless else was hit
        var table = document.getElementById(tableID);
        var rowCount = table.rows.length;
        var new_row = table.rows[rowCount - 1];
        var row = table.insertRow(rowCount);
        var colCount = table.rows[0].cells.length;

        for (var i = 0; i < colCount; i++) {
            var newcell = row.insertCell(i);
            newcell.innerHTML = new_row.cells[i].innerHTML;
        }
    }
}​