javascript check for null variables
var myVar=null;
if(myVar === null){
//I am null;
}
if (typeof myVar === 'undefined'){
//myVar is undefined
}javascript check for null variables
var myVar=null;
if(myVar === null){
//I am null;
}
if (typeof myVar === 'undefined'){
//myVar is undefined
}javascript null vs undefined
/* In Javascript,
* null: a value explicitly set by the programmer for the intentional lack of value.
* undefined: a value implictily or explicitly set for the intentional lack of value.
*/
console.log(null == undefined) // true
console.log(null === undefined) // false
let a = null
console.log(a) // null
let c;
let d = undefined;
console.log(c, d) // undefined undefined
console.log(typeof null) // Object
console.log(typeof undefined) // undefinednull undefined
Undefined used for unintentionally missing values.
Null used for intentionally missing values.js null vs undefine
var TestVar = null;
alert(TestVar); //shows null
alert(typeof TestVar); //shows objectnull vs undefined
//loosely equal (compare values between two variables)
null == undefined // true ( null => 0 , undefined => NAN)
//strictly not equal (compare both type and value)
null === undefined // false (typeof null => object , typeof undefined => undefined)
null !== undefined // true (typeof null => object , typeof undefined => undefined)js null vs undefine
var TestVar;
alert(TestVar); //shows undefined
alert(typeof TestVar); //shows undefinedCopyright © 2021 Codeinu
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