How to determine whether it is a number in js

JS method to determine whether it is a number: 1. Use the isNaN() function to determine whether it is a number; 2. Use regular expressions to determine whether it is a number; 3. Use the return value of parseFloat() to realize the judgment.

The operating environment of this tutorial: Windows 7 system, JavaScript version 1.8.5, DELL G3 computer.

Method 1: Use the isNaN() function

The isNaN() function is a global function that comes with js. The isNaN() function is used to check whether its parameter is a non-number. value.

If value x is a special non-numeric value NaN (or can be converted to such a value), the returned value is true; if value x is another value, false is returned.

The disadvantage of isNaN() is that null, space and empty string will be treated as 0

NaN: Not a Number
<script>
document.write(isNaN(123));  //数字
document.write(isNaN(-1.23));  //数字
document.write(isNaN(5-2));  //数字
document.write(isNaN(0));  //数字
document.write(isNaN("Hello"));  //字符串
document.write(isNaN("2005/12/12"));  //字符串
</script>

Output:

false
false
false
false
true
true

Disadvantage: isNaN() will treat null, Spaces and empty strings are treated as 0, so the check is not strict.

So process it and use it with the typeof operator.

Example:

// true:数值型的，false：非数值型
function myIsNaN(value) {
   document.write((typeof value === &#39;number&#39; && !isNaN(value))+"<br>");
}
myIsNaN(10); 
myIsNaN(null); 
myIsNaN( );
myIsNaN();

Output:

true
false
false
false

Method 2: Use regular expression

(1), check as long as If it is a number (including positive and negative integers, 0 and positive and negative floating point numbers), it will return true

/**
* 校验只要是数字（包含正负整数，0以及正负浮点数）就返回true
**/
function isNumber(val){
    var regPos = /^[0-9]+.?[0-9]*/; //判断是否是数字。
  
    if(regPos.test(val) ){
        return true;
    }else{
        return false;
    }
}

(2). If it is a positive and negative number, it will return true

/**
* 校验正负正数就返回true
**/
function isIntNum(val){
    var regPos = / ^\d+$/; // 非负整数 
    var regNeg = /^\-[1-9][0-9]*$/; // 负整数
    if(regPos.test(val) && regNeg.test(val)){
        return true;
    }else{
        return false;
    } 
}

Method 3 : Use the return value of parseFloat()

parseFloat() function to parse a string and return a floating point number.

This function specifies whether the first character in the string is a number. If it is, the string is parsed until it reaches the end of the number, and the number is returned as a number rather than as a string.

Usage: Parse the string specified in the parameter into a floating point number and return it.

/**
* 验证数据 是数字：返回true；不是数字：返回false
**/
function Number(val) {
　　if (parseFloat(val).toString() == "NaN") {
　　　　
　　　　return false;
　　} else {
　　　　return true;
　　}
}
//isNaN(val)不能判断空串或一个空格
//如果是一个空串、空格或null，而isNaN是做为数字0进行处理的，
//而parseInt与parseFloat是返回一个错误消息，这个isNaN检查不严密而导致的。

Recommended study: "js Basic Tutorial"

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