How to determine whether a string is a number in es6

3 ways to judge: 1. Use the isFinite() function, the syntax is "isFinite (string)", return true to indicate that it is a number, and return false to indicate that it is not a number. 2. Use the isNaN() function, the syntax is "isNaN (string)", return true to indicate that it is not a number, and return false to indicate that it is a number. 3. Use the test() function and regular expressions, the syntax is "/^[0-9] .?[0-9]*/.test(string)", and return true to represent a number.

The operating environment of this tutorial: Windows 7 system, ECMAScript version 6, Dell G3 computer.

es6 3 ways to determine whether a string is a number

Method 1: Use the isFinite() function

isFinite() function is used to check whether its parameter is infinity, which can also be understood as whether it is a finite number.

isFinite(value)

That is, whether the parameter value passed in is a finite number.

Returning true means it is a number, returning false means it is not a number

console.log(isFinite("123")); // true
console.log(isFinite("beline")); //false
console.log(isFinite(NaN)); // false
console.log(isFinite(undefined)); // false

##Method 2: Use the isNaN() function

isNaN() function is used to check whether its argument is a non-numeric value.

isNaN(value)

If the parameter value is NaN or a non-numeric value such as a string, object, or undefined, it returns true, otherwise it returns false, which means it is a valid number

console.log(isNaN(1)); // false
console.log(isNaN("12.3")); // false
console.log(isNaN("beline")); //true
console.log(isNaN(NaN)); // true
console.log(isNaN(undefined)); // true

Method 3: Using the test() function and regular expressions

The test() method is used to detect whether a string matches a certain pattern.

If the string Returns true if there is a matching value, otherwise returns false.

Regular expression:

/^[0-9] .?[0-9]*/, determine whether it is a number

As long as If it is a number (including positive and negative integers, 0 and positive and negative floating point numbers), it returns true, otherwise it returns false.

var patt=/^[0-9]+.?[0-9]*/;
console.log(patt.test(12)); // true
console.log(patt.test("12.3")); // true
console.log(patt.test("beline")); //false
console.log(patt.test(NaN)); // false
console.log(patt.test(undefined)); // false

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