如何檢查我是否在javascript中提交空白輸入？我寫了一個程式，但它不起作用

我已經使用腳本標簽在 HTML 檔案中撰寫了一個 javascript 代碼，我想知道我的輸入是大于還是小于 10 或等于 10 或任何空白輸入。我使用 if-else 方法來解決這個問題，但是我的最后一個 else if 條件“您的輸入為空”沒有以任何方式輸出。

//f1 function will run when some hit the submit button
function f1() {
  //here we are taking the value of the input field using id "myinput" in the variable called myinputvar
  var myinputvar = document.getElementById("myinput").value;
  if (myinputvar > 10) {
    document.getElementById("txt").innerHTML = "Your input number is greater than 10";
  } else if (myinputvar < 10) {
    document.getElementById("txt").innerHTML = "Your input number is less than 10";
  } else if (myinputvar = 10) {
    document.getElementById("txt").innerHTML = "Your input number is 10";
  } else if (myinputvar = " ") {
    document.getElementById("txt").innerHTML = "Your input is blank";
  }
}

<!-- this is the input tag to take inputs from user -->
Enter a integer number between 0 to anynumber = <input type="text" id="myinput"><br><br>
<!-- this is the button to submit the value -->
<button onclick="f1()">submit</button>
<!-- this is the heading tag to print the output -->
<h1 id="txt"></h1>

uj5u.com熱心網友回復：

僅檢查空白輸入的一般方法是使用正則運算式模式^\s*$。示例代碼：

if (/^\s*$/.test(inputvar)) {
    document.getElementById("txt").innerHTML = "Your input is blank";
}

uj5u.com熱心網友回復：

包裝成一個表格并使其成為必需的

也投射到數字

document.getElementById("myForm").addEventListener("submit", function(e) {
  e.preventDefault(); // stop submission
  //here we are taking the value of the input field using id "myinput" in the variable called myinputvar
  var myinputvar =  document.getElementById("myinput").value; // make it a number
  if (myinputvar > 10) {
    document.getElementById("txt").innerHTML = "Your input number is greater than 10";
  } else if (myinputvar < 10) {
    document.getElementById("txt").innerHTML = "Your input number is less than 10";
  } else if (myinputvar = 10) {
    document.getElementById("txt").innerHTML = "Your input number is 10";
  } else if (myinputvar = " ") {
    document.getElementById("txt").innerHTML = "Your input is blank";
  }
})

<form id="myForm">
  Enter a integer number between 0 to anynumber =
  <input type="text" required id="myinput"><br><br>
  <button>submit</button>
</form>
<h1 id="txt"></h1>

uj5u.com熱心網友回復：

注意不要使用快捷方式：

if (inputvar) {
    // this won't catch "0"!
}

但更合適

if (inputvar === "") {
    // is empty
}

當然，如果您想將數字作為輸入處理，您應該首先檢查這種情況。

uj5u.com熱心網友回復：

Check if given input value is valid number or not

    function isNumber(n){ return /^-?[\d.] (?:e-?\d )?$/.test(n); }

uj5u.com熱心網友回復：

> As @Tim Biegeleisen mentioned, this is worked in this way,

var myinputvar = document.getElementById("myinput").value;
            if (/^\s*$/.test(myinputvar)) {
                document.getElementById("txt").innerHTML = "Your input is blank";
            } else {
                if (myinputvar > 10) {
                    document.getElementById("txt").innerHTML = "Your input number is greater than 10";
                } else if (myinputvar < 10) {
                    document.getElementById("txt").innerHTML = "Your input number is less than 10";
                } else if (myinputvar = 10) {
                    document.getElementById("txt").innerHTML = "Your input number is 10";
                }
            }

uj5u.com熱心網友回復：

您可以使用 ASCII 代碼來檢查

else if(myinputvar.carCodeAt(0) === 13) {
    document.getElementById("txt").innerHTML = "Your input is blank";
}

13是回車鍵的ASCII碼 https://www.asciitable.com/

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