An article to talk about NaN in JavaScript

In JavaScript,NaNis a special numeric value (the result oftypeof NaNisnumber), which isnot a numberis an abbreviation, indicating that it is not a legal number.

1. Generation of NaN:

• A number that cannot be parsed

Number('abc') // NaN Number(undefined) // NaN

• Failed operation

Math.log(-1) // NaN Math.sqrt(-1) // NaN Math.acos(2) // NaN

• An operator isNaN

NaN + 1 // NaN 10 / NaN // NaN

2. Notes

NaNisthe only value thatis not equal to itself:

NaN === NaN // false

3. How To identify NaN

we can use the global functionisNaN()to determine whether a value is anon-number(not used to determine whether Not the valueNaN):

isNaN(NaN) // true isNaN(10) // false

Why isisNaN()not used to determine whether it is the valueNaN? BecauseisNaNdoesn't work on non-numbers, the first thing it does is convert these values to numbers, which may result inNaN, and then the function will incorrectly returntrue:

isNaN('abc') // true

So we want to make sure that this value isNaN, we can use the following two methods:

• Method 1: ChangeisNaN()is combined withtypeofto determine

function isValueNaN(value) { return typeof value === 'number' && isNaN(value) }

• Method 2: Whether the value is not equal to itself (NaNisOnlyThe value with such characteristics)

function isValueNaN(value) { return value !== value }

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