How to determine whether a specified value is a number in javascript

Judgment method: 1. Use the isNaN() function, the syntax "isNaN(value)", if the value is a number, return false; 2. Use the return value of typeof, the syntax "typeof(value)", if If the returned value is "Number", it is a number; 3. Use regular expressions to judge.

The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.

javascript determines whether the specified value is a number

Method 1: isNaN() function

The isNaN() function determines whether a value is Not-a-Number. This function returns true if the value is equal to NaN. Otherwise return false.

var c="hello"; //字符串
isNaN(c); //返回一个true;
var c=10; //数字
isNaN(c);//返回一个false

The disadvantage of isNaN() is that null, space and empty string will be processed as 0, which needs to be optimized

/**
*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; 
　　} 
}

Method 2: Use the return value of typeof

Verification method: If the returned value is Number, it is a number; if the return value is String or other, it is not a number. As shown below:

var a=123;
var b='123abc';
typeof(a) //Number
typeof(b) //String

Method 3: Use regular expressions

(1), check as long as it is a number (including positive and negative integers, 0 and positive and negative floats Points) 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 the positive and negative numbers are verified, true will be returned

/**
* 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;
    } 
}

[Recommended learning: javascript advanced tutorial]

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