Question

非常直接的我想做的事情：

如果输入为0，则表示他们没有输入数字应该告诉你。
当输入为7时，应该说你做对了。
别的，它应该告诉你，你弄错了。

但无论输入是什么，它只输出“7是正确的”线，我无法弄清楚出了什么问题。

<script type="text/javascript">
function problem2 ()
{
var number = 0;
var text=document.getElementById("output");
number = prompt("Enter a number between 1 and 10 please" , 0);
if (number = 0)
    {
     text.value = "You didn't enter a number!";
    }
if (number = 7)
    {
     text.value = "7 is correct!";
    }
else
    {
     text.value = "Sorry, ", input, "is not correct!";
    }
}
</script>
<input type="button" value="Click here" onclick="problem2()">
<input id="output" type="text">

Answer 1

您正在使用=进行分配。使用==或===。

if( 0 == number ){

  text.value = "You didn't enter a number!";
}

另外，要小心你的支具位置。 Javascript喜欢自动添加分号到行尾。 Source

Answer 2

您使用赋值运算符作为条件而不是比较运算符：

if (number = 0) // falsy. Same as if (false)
    {
     text.value = "You didn't enter a number!";
    }
if (number = 7) // truthy. Same as if (true)
    {
     text.value = "7 is correct!";
    }
else
    {
     text.value = "Sorry, ", input, "is not correct!";
    }

或者，您可以使用开关并更轻松地组织条件：

switch (number) {
    case 0: 
        text.value = "You didn't enter a number!";
        break;

    case 7:
        text.value = "7 is correct!";
        break;

    default:
        text.value = "Sorry, ", input, "is not correct!";
        break;
}

Answer 3

以下是一些代码，其中包含一些修复和改进（我评论了我所做的更改）：

function problem2 (){
    //I multiplied by * 1 to work with numbers, also used || to default to 0 in case of NaN
    var num = (prompt("Enter a number between 1 and 10 please" , 0) * 1) || 0;
    var msg = "";

    if (!num){ //I prefer this over 'num == 0'
         msg = "You didn't enter a number!";
    //you should use 'else if' in this case
    }else if (num == 7){//'=' is for assignment, use '==' or '===' instead
         msg = "7 is correct!";
    }else{
        //you had an undefined var 'input', you probably meant 'num'
        //you also were connecting var and strings using commas, use '+' instead
         msg = "Sorry, " + num + " is not correct!"; //added a space in ' is'
    }

    //no need to store the element in a var anymore :D
    document.getElementById("output").value = msg;
}

另外，还可以进行两项更改：

只有一个var（例如var something = "", somethingElse = 99;）
从头开始分配默认文字，例如var msg = "default"，然后移除else

注意：我做的一个未记录的更改是重命名一些变量，我鼓励大家停止使用像number, text, string这样的变量，如果你有这个坏习惯，你最终会使用非法var错误的名字。

Javascript if语句不起作用

3 个答案: