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Methods for JavaScript to determine whether it is a number: 1. Use the [isNaN()] function; 2. Use regular expressions; 3. Use the return value of [parseFloat()].
The operating environment of this tutorial: Windows 7 system, JavaScript version 1.8.5, DELL G3 computer.
JavaScript method to determine whether it is a number:
Method 1: Use isNaN() function
isNaN() function It is a global function that comes with js. The isNaN() function is used to check whether its parameter is a non-numeric 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 ----false document.write(isNaN(-1.23)); //数字 ----false document.write(isNaN(5-2)); //数字 ----false document.write(isNaN(0)); //数字 ----false document.write(isNaN("Hello")); //字符串 ----true document.write(isNaN("2005/12/12")); //字符串----true </script>
Disadvantage: isNaN() will 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) { return (typeof value === 'number' && !isNaN(value)); } myIsNaN(10); ----true myIsNaN(null); ----false myIsNaN( ); ----false myIsNaN(); ----false
Note: If it is '36.3', typeof value === 'number', it will return false. If you want string type numbers to also return true, you can use the following Method 3
Method 2: Use regular expression
(1) to check as long as it is a number (including positive and negative integers, 0 and positive and negative floating point numbers) It returns 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 the positive and negative numbers are verified, it returns 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 parses a string and returns 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) cannot judge an empty string or a space
If it is an empty string, space or null, and isNaN is processed as a number 0,
And parseInt and parseFloat return an error message, which is caused by the loose isNaN check.
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