How does javascript determine whether a specified value is a number or not

Editor to share with you javascript how to judge whether the specified value is a number, I believe most people do not know much about it, so share this article for your reference, I hope you can learn a lot after reading this article, let's go to know it!

Judgment method: 1, the use of isNaN () function, syntax "isNaN (value)", if the value is a number, then return false;2, using the return value of typeof, syntax "typeof (value)", if the return value is "Number", it is a number; 3, use regular expression to judge.

The operating environment of this tutorial: windows7 system, javascript1.8.5 version, Dell G3 computer.

Javascript determines whether the specified value is a number.

Method 1:isNaN () function

The isNaN () function determines whether the value is nonnumeric (Not-a-Number). If the value is equal to NaN, this function returns true. Otherwise, false is returned.

Var c = "hello"; / / string isNaN (c); / / returns a true;var cantilever 10; / / numeric isNaN (c); / / returns a false

The disadvantage of isNaN () is that null, spaces, and empty strings are treated as zeros and need to be optimized.

/ * determine whether it is a number * * / function isRealNum (val) {/ / isNaN () function processes empty string spaces and NUll as 0, so remove first, if (val = = "" | val = = null) {return false } if (! isNaN (val)) {/ / for an empty array and an array with only one numeric member or a string full of numbers, / / isNaN returns false, for example: '123', [], [2], ['123'], isNaN returns false, / / so if you don't need val to include these special cases Then the judgment is rewritten to 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 follows:

Var / Numbertypeof (b) / / String

Method 3: use regular expressions

(1) true is returned as long as the check is a number (including positive and negative integers, 0 and positive or negative floating point numbers)

/ * check returns true**/function isNumber (val) {var regPos = / ^\ d + (\.\ d +) as long as it is a number (including positive and negative integers, 0 and positive or negative floating point numbers)? $/ / / Nonnegative floating point number var regNeg = / ^ (- (([0-9] +\. [0-9] * [1-9] [0-9] *) | ([0-9] * [1-9] [0-9] *. [0-9] +) | ([0-9] * [1-9] [0-9] *)) $/ / / negative floating point if (regPos.test (val) & & regNeg.test (val)) {return true;} else {return false;}}

(2) check positive or negative numbers and return true

/ * * check a positive or negative number and return true**/function isIntNum (val) {var regPos = / ^\ dprinter; / / non-negative integer var regNeg = / ^\-[1-9] [0-9] * $/; / negative integer if (regPos.test (val) & regNeg.test (val)) {return true;} else {return false }} above is all the content of the article "how to determine whether the specified value is a number or not by javascript". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!