Question

我正在构建一个计算器，必须这样做，以便每次单击操作员按钮时，字体都会变为红色。

function changeBtnColor(entry){
    if(entry == '+'){
        calculator.getElementById("buttonAdd").style.fontcolor = 'red';
        calculator.answer.value +=' + ';
    }
    if(entry == '-'){
        calculator.getElementById("buttonSub").style.fontcolor = 'red';
        calculator.answer.value +=' - ';
    }
    if(entry == '*'){
        calculator.getElementById("buttonMult").style.fontcolor = 'red';
        calculator.answer.value +=' * ';
    }
    if(entry == '/'){
        calculator.getElementById("buttonDiv").style.fontcolor = 'red';
        calculator.answer.value +=' / ';
    }
}

我如何调用此js函数的示例是：

<form id = "calculator" name=”calculator”>
        <table id = "myTable" border = "2">
            <tbody>
                <tr>
                    <td colspan = "4">
                         <input id = "answer" type="text" name="answer"/> 
                    </td>
                 </tr>
                 <tr>
                    <td><input id = "button7" type="button" value="7" onClick="calculator.answer.value +='7'"></td>
                    <td><input id = "button8" type="button" value="8" onClick="calculator.answer.value +='8'"></td>
                    <td><input id = "button9" type="button" value="9" onClick="calculator.answer.value +='9'"></td>
                    <td><input id = "buttonAdd" type="button" value="+" onClick="changeBtnColor('+')"></td>
                 </tr>

执行此操作时，出现错误：

calculator.getElementById is not a function
at changeBtnColor (calculator.js:44)
at HTMLInputElement.onclick (calculator.html:21)

有人对此错误有任何建议或可以告诉我为什么发生此错误吗？谢谢！

Answer 1

函数“ getElementById”是为文档对象而不是表单元素定义的。

document.getElementById("buttonAdd")

在JavaScript中更改字体颜色时出现问题

1 个答案: