The JavaScript Interview Handbook: 100+ Interview Questions/

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Solution Review: "strict" Mode

Solution Review: "strict" Mode

In this lesson, we will discuss the solutions to the questions in the previous lesson.

We'll cover the following...

Question 1: Solution review #

In the previous lesson, you were given the following code:

Javascript (babel-node)
"use strict"
var obj1 = {};
Object.defineProperty(obj1, 'x', { value: 42, writable: false });
obj1.x = 9;

For the code above, you had to answer the following question.

Explanation #

Let’s run the code to see what happens.

Node.js
"use strict"
var obj1 = {};
Object.defineProperty(obj1, 'x', { value: 42, writable: false });
obj1.x = 9;

As you can see, an error is thrown when the code is run; this means Option A is correct. Why do you see an error?

The answer might seem obvious; since, on line 3, when we define the property x, we set its writable property to false; this means it is a read-only property.

On ...