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 

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 === 'number' && !isNaN(value))+"
"); } 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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