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JavaScript null vs undefined vs blank vs value

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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