ioncreature/js-interview

Questions for interview for JS

1. ES5 features

   • Explain array methods(map, filter, some, every, reduce, reduceRight, forEach)

     What does this code do?

     emailsString.split( /[,;\s]+/ ).every( email => isEmail(email) );

     Rewrite it with .some() method

   • Object methods

     • Describe property attributes and Object.defineProperty, Object.getOwnPropertyDescriptor methods

       Write method join:

       var a = {a: 1, b: 2, c: 3};
       a.join() // output: a,b,c

       // possible solution:
       Object.defineProperty( Object.prototype, 'join', {
           value(){
               return Object.keys( this ).join( ',' );
           },
           enumerable: false
       });

     • Explain difference between Object.keys and Object.getOwnPropertyNames:

       var a = {q: 1};
       Object.defineProperty( a, 'xxx', {value: 'yyy', enumerable: false} );
       Object.keys(a); // what it returns? 
       Object.getOwnPropertyNames(a); // what it returns? 

     • Setters and Getters

   • Strict mode restrictions

     • Global scope restrictions

     (function(){
         "use strict";
         x = 100;
     })();

2. Closures

3. Context

4. Scope

   • What is the result of:

   Object.prototype.x = 10;
   var y = 20;
   (function(){
       console.log( x, y );
   })();

5. Write function "reverse" for objects (have to work as for arrays)

   // possible solution
   function reverse( obj ){
       return Object.keys( obj ).reverse().reduce( (res, i) => {
           res[i] = obj[i];
           return res;
       }, {} );
   }

6. Write function "pop" for objects (have to work as for arrays)

   // possible solution
   function pop( obj ){
       var keys = Object.keys( obj );
       if ( !keys.length )
           return;
       
       var key = keys[keys.length - 1],
       val = obj[key];
       
       delete obj[key];
       return val;
   }