Junior Garcia
Junior Garcia@jrgarciadev

Top JavaScript Interview Questions

A selection of crucial JavaScript interview topics to test your skills. Prepare for your next interview with these top questions, designed to evaluate your knowledge and problem-solving abilities.

Here's a rephrased and reordered version of your questions to make them easier to understand and ordered by difficulty and similarity:

Basic Questions

Question 1. What will be the output of the following code?

 
var output = (function(x) {
  delete x;
  return x;
})(0);

console.log(output);
Answer

The output will be 0. The delete operator is used to remove properties from objects. Here, x is a local variable, not an object property, so the delete operator has no effect on it.

Question 2. What will be the output of the following code?

 
var x = 1;
var output = (function() {
  delete x;
  return x;
})();

console.log(output);
Answer

The output will be 1. The delete operator is used to remove properties from objects. Here, x is a global variable of type number, not an object property, so the delete operator has no effect on it.

Question 3. What will be the output of the following code?

 
var x = { foo : 1 };
var output = (function() {
  delete x.foo;
  return x.foo;
})();

console.log(output);
Answer

The output will be undefined. The delete operator removes the foo property from the x object. After deletion, x.foo no longer exists, so it returns undefined.

Intermediate Questions

Question 4. How can you check if an object is an array in JavaScript?
Answer

You can check if an object is an array using several methods:

  1. Using Array.isArray:
Array.isArray(arrayList);
  1. Using Object.prototype.toString:
if(Object.prototype.toString.call(arrayList) === '[object Array]') {
  console.log('Array!');
}
  1. Using jQuery (if available):
if($.isArray(arrayList)) {
  console.log('Array');
} else {
  console.log('Not an array');
}

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