js determines whether the value is a number

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

The operating environment of this article: windows7 system, DELL G3 computer

JS determines whether the value is a number

1. Use the isNaN() function

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

NaN: Not a Number

/**
*判断是否是数字
*
**/

function isRealNum(val){
    // isNaN()函数 把空串 空格 以及NUll 按照0来处理 所以先去除，    
　　if(val === "" || val ==null){
        return false;
　　}
   if(!isNaN(val)){　　　　
　　//对于空数组和只有一个数值成员的数组或全是数字组成的字符串，isNaN返回false，例如：'123'、[]、[2]、['123'],isNaN返回false,   //所以如果不需要val包含这些特殊情况，则这个判断改写为if(!isNaN(val) && typeof val === 'number' )
　　　 return true; 　　}　else{ 　　　　return false; 　　} }

The most correct way to use the isNaN() function to determine whether a value is a number is:

// true:数值型的，false：非数值型
  function myIsNaN(value) {    return typeof value === 'number' && !isNaN(value);
  }

isNaN() detailed explanation [Recommended ：js Basic Tutorial】

Reference link: https://wangdoc.com/javascript/types/number.html#isnan

For empty arrays and For an array with only one numeric member, isNaN returns false.

isNaN([]) // false
isNaN([123]) // false
isNaN(['123']) // false

The reason why the above code returns false is that these arrays can be converted into numerical values ​​by the Number function. Please refer to the chapter "Data Type Conversion".

Therefore, it is best to determine the data type before using isNaN.

function myIsNaN(value) {  return typeof value === 'number' && !isNaN(value);
}

2. Use regular expressions

(1), to check as long as 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 = /^\d+(\.\d+)?$/; //非负浮点数
    var regNeg = /^(-(([0-9]+\.[0-9]*[1-9][0-9]*)|([0-9]*[1-9][0-9]*\.[0-9]+)|([0-9]*[1-9][0-9]*)))$/; 
    //负浮点数
    if(regPos.test(val) && regNeg.test(val)){        
    return true;
    }else{        
    return false;
    }

}

(2), If it checks the positive and negative numbers, 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;
    } 
}

3. Use parseFloat() function

 (parseFloat(val).toString() == "NaN"

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