How to determine if a value is a number in javascript

Method: 1. test() with regular expression; 2. parseFloat() function, syntax "parseFloat(value).toString()=="NaN""; 3. isNaN() function, syntax "typeof value ==='number'&&!isNaN(value)".

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

Method 1: Use test() regular expression

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

/**
* 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;
    }
}

Method 2: Use parseFloat() function

/**
* 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;
　　}
}

Method 3: Use isNaN() function

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

isNaN( )Detailed explanation

For empty arrays and arrays 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, before using isNaN, it is best to determine the data type.

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

[Recommended learning: javascript advanced tutorial]

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