Question

How to use the in operator to check if a specified property is in a specified object in JavaScript

Answer 1

var programming = ["JavaScript", "Java", "C#", "PHP"]; 
        
var b = "Java" in programming;  
document.write(b + "<br />");

b = 0 in programming;  
document.write(b + "<br />");

b = 3 in programming;  
document.write(b + "<br />");

b = 4 in programming; 
document.write(b + "<br />");

b = "length" in programming;
document.write(b + "<br />");
document.write(programming.length + "<br />");

b = "join" in programming;  
document.write(b + "<br />");

 
/*
run:

false
true
true
false
true
4
true
 
*/

 

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Answer 2

var e = {name:"tom bankester", profession:"programmer", salary:13990, company:"x3z"};
        
var b = "name" in e; 
document.write(b + "<br />");

b = 1 in e;
document.write(b + "<br />");

b = "profession" in e;
document.write(b + "<br />");

b = "age" in e;
document.write(b + "<br />");

 
/*
run:

true
false
true
false
 
*/

 

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Answer 3

var b = "PI" in Math;
document.write(b + "<br />");

b = "length" in String;    
document.write(b + "<br />");

var b = "pow" in Math;
document.write(b + "<br />");

b = "NaN" in Number;  
document.write(b + "<br />");


 
/*
run:

true
true
true
true
 
*/

 

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