Node.js Tutorial - Node.js Data Type

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Node.js is highly performant, and it uses JavaScript because JavaScript supports first-class functions and closures.

Node.js has a few core types: number , boolean , string , and object.

The value undefined means that a value has not been set yet or simply does not exist:

var x;
console.log(x);

The code above generates the following result.

Null

null is an explicit assertion that there "is no value":

var y;
console.log(y);

y = null ;
console.log(y);

The code above generates the following result.

typeof

To see the type of anything in JavaScript, use the typeof operator:

console.log(typeof 10);
console.log(typeof "hello");
console.log(typeof function () { var x = 20; });

The code above generates the following result.

Constants

The standard practice is to use uppercase letters and variable declarations:

var SECONDS_PER_DAY = 86400;
console.log(SECONDS_PER_DAY);

Type Comparisons and Conversions

JavaScript has both the equality operator == and the precise equality operator ===.

console.log(234 == '234');
console.log(234 === '234');
console.log(234234.235235 == 'cat');
console.log("cat" == "CAT");
console.log("cat".toUpperCase() == "CAT");

The code above generates the following result.

A number of different values evaluate to false.

console.log('' == false == null == undefined == 0);
console.log(null === undefined);

To check arguments to functions:

function fine(param) {
   if (param == null || param == undefined || param == '')
      throw new Error("Invalid Argument");
}
function better(param) {
    if (!param) 
       throw new Error("Invalid Argument");
}

Pay more attention to the primitive wrapper.

var x = 234;
var x1 = new Number(234);
console.log(typeof x);
console.log(typeof x);
console.log(x1 == x);
console.log(x1 === x);

The code above generates the following result.

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