What does isnan mean in js

What is isNaN?

isNaN is a global function in JavaScript that checks whether a value is not a number (NaN).

Detailed description:

isNaN The function accepts a value as a parameter and returns a Boolean value:

• If the argument is a NaN value, isNaN returns true.
• If the parameter is not a NaN value, isNaN returns false.

NaN is a special value that represents an uncertain numeric value. NaN values ​​are produced when a mathematical operation fails to produce a meaningful result. For example:

<code class="js">console.log(isNaN(NaN)); // true
console.log(isNaN(1)); // false
console.log(isNaN("hello")); // true</code>

Usage example:

isNaN function can be used to validate input to ensure that the number format entered by the user is correct. For example:

<code class="js">const input = prompt("请输入一个数字：");
if (isNaN(input)) {
  alert("输入无效，请输入一个数字。");
} else {
  const number = parseInt(input);
  // 处理有效的数字
}</code>

Note:

• NaN is not a number, so it is not the same as other numeric values ​​(including 0 )different.
• isNaN applies not only to numeric literals, but also to variables or expressions that hold numeric values.
• Even if the input value is an empty string, isNaN will return true.

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