JavaScript null vs undefined vs blank vs value

Every JavaScript beginner gets confused when checking JavaScript variable, value is defined or not if defined then value is blank or has a value. So I am going to explain this.

undefined: it means a variable has declared but has not assigned a value, let me explain with an examples

var name; console.log(name); //output will be undefined console.log(typeof name); //output will be undefined

So JavaScript variable undefined condition should be

if( typeof name !== 'undefined' ) { // your code }

null: it means variable is assigned with null which means a variable has no value, let’s see the example for better understanding

var name =null; considers.log(name); //output will be null console.log(typeof name) //output will be object

if you want to check whether the value is assigned or not always check with this condition

if( typeof value == 'undefined' || variable == null ){ // your code }

now lets check variable has a string or number value assigned

var x = 'Abhay' var y = 1; 
console.log(typeof x); 
//output will be a string so for string checking condition will be if( typeof value === 'string'){ 
// your code 
} 
console.log( typeof y);
//output will be number so for number checking condition will be 
if( typeof value === 'number'){ 
// your code 
}

I hope this will be helpful to JavaScript variable assignment checking.

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Originally published at https://codinghub.net.