isNaN() in JavaScript.

The 𝐢𝐬𝐍𝐚𝐍() function is a 𝐛𝐮𝐢𝐥𝐭-𝐢𝐧 𝐟𝐮𝐧𝐜𝐭𝐢𝐨𝐧 in JavaScript that is used to determine whether a 𝐕𝐀𝐋𝐔𝐄 is 𝐍𝐚𝐍 (𝐍𝐨𝐭-𝐚-𝐍𝐮𝐦𝐛𝐞𝐫) or not.

𝐓𝐡𝐞 𝐢𝐬𝐍𝐚𝐍() 𝐦𝐞𝐭𝐡𝐨𝐝:
1-returns a 𝐛𝐨𝐨𝐥𝐞𝐚𝐧 𝐯𝐚𝐥𝐮𝐞 (true or false).
2-return 𝐭𝐫𝐮𝐞 if a value is NaN, otherwise 𝐟𝐚𝐥𝐬𝐞.
3-𝐜𝐨𝐧𝐯𝐞𝐫𝐭𝐬 𝐭𝐡𝐞 𝐕𝐀𝐋𝐔𝐄 𝐓𝐎 𝐀 𝐍𝐔𝐌𝐁𝐄𝐑 𝐛𝐞𝐟𝐨𝐫𝐞 𝐭𝐞𝐬𝐭𝐢𝐧𝐠 𝐢𝐭.

𝐒𝐲𝐧𝐭𝐚𝐱:
isNaN(value)

𝐇𝐨𝐰 𝐢𝐬𝐍𝐚𝐍() 𝐰𝐨𝐫𝐤𝐬?

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When the 𝐢𝐬𝐍𝐚𝐍() function is called with an 𝐚𝐫𝐠𝐮𝐦𝐞𝐧𝐭 𝐭𝐡𝐚𝐭 𝐢𝐬 𝐧𝐨𝐭 𝐚 𝐧𝐮𝐦𝐛𝐞𝐫, 𝐢𝐭 𝐟𝐢𝐫𝐬𝐭 𝐭𝐫𝐢𝐞𝐬 𝐭𝐨 𝐜𝐨𝐧𝐯𝐞𝐫𝐭 𝐭𝐡𝐞 𝐚𝐫𝐠𝐮𝐦𝐞𝐧𝐭 𝐭𝐨 𝐚 𝐧𝐮𝐦𝐛𝐞𝐫. If the argument can be converted to a valid number, the function returns 𝐟𝐚𝐥𝐬𝐞, indicating that the argument is not 𝐍𝐚𝐍.

E.g isNaN(𝐯𝐚𝐥𝐮𝐞) ->isNaN(𝐍𝐮𝐦𝐛𝐞𝐫(value))

Examples:

//JavaScript Surgeon

//A-Numbers
isNaN(2); //false : 2 is a number
isNaN(2.4); //false : 2.4 is a number
isNaN(2–1); //false : 2–1=1 which is not NaN

//B-Falsy Values
isNaN(0); //false : 0 is a number
isNaN(-0); //false : -0 is a number
isNaN(false); //false : false->0 which is not NaN
isNaN(""); //false : the empty string is converted to 0 which is not NaN
isNaN(NaN); //true : NaN is not equal to any value, including itself
isNaN(undefined); //true : undefined cannot be converted into number, if we try it gives NaN
isNaN(null); //false : null is coerced to a number->0 which is not NaN

//Truthy Values
isNaN(true) //false : true ->1 (a number)
isNaN({}); //true : {} cannot be converted into number, if we try it gives NaN
isNaN([]); //false : [] when it is coerced to a number is becomes 0 (a number)

// Strings
isNaN(""); //false : the empty string is converted to 0 which is not NaN
isNaN(" "); //false : a string with spaces is converted to 0 which is not NaN
isNaN("37"); //false : "37" is converted to the number 37 which is not NaN
isNaN("37.37"); //false : "37.37" is converted to the number 37.37 which is not NaN
isNaN("2–1"); //true : "2–1" is a string
isNaN("37,5"); //true : "37,5" is a string
isNaN("123ABC"); //true : Number("123ABC") is NaN

// Dates
isNaN("14/04/2023"); //true : it is a string
isNaN(new Date()); //false : Date objects can be converted to a number (timestamp)
isNaN(new Date().toString()); //true : the string representation of a Date object cannot be parsed as a numberj

Comparisons:

isNaN(2); //false : 2 (a number)
isNaN("2"); //false : "2" is converted into 2 (a number)

isNaN(2–1); //false : 2–1=1 (a number)
isNaN("2–1"); //true : "2–1" is a string

isNaN(false); //false : false->0 (a number)
isNaN(true); //false : true ->1 (a number)

isNaN(""); //false : the empty string is converted to 0 which is not NaN
isNaN(" "); //false : a string with spaces is converted to 0 which is not NaN

isNaN(NaN); //true : NaN is not equal to any value, including itself
isNaN(undefined); //true : undefined cannot be converted into number, if we try it gives NaN
isNaN(null); //false : null is coerced to a number->0 which is not NaN

isNaN({}); //true : {} cannot be converted into number, if we try it gives NaN
isNaN([]); //false : [] when it is coerced to a number is becomes 0 (a number)