freeCodeCamp/curriculum/challenges/english/02-javascript-algorithms-and-data-structures/es6/prevent-object-mutation.md

id, title, challengeType, forumTopicId, dashedName

id	title	challengeType	forumTopicId	dashedName
598f48a36c8c40764b4e52b3	Prevent Object Mutation	1	301207	prevent-object-mutation

--description--

As seen in the previous challenge, const declaration alone doesn't really protect your data from mutation. To ensure your data doesn't change, JavaScript provides a function Object.freeze to prevent data mutation.

Once the object is frozen, you can no longer add, update, or delete properties from it. Any attempt at changing the object will be rejected without an error.

let obj = {
  name:"FreeCodeCamp",
  review:"Awesome"
};
Object.freeze(obj);
obj.review = "bad";
obj.newProp = "Test";
console.log(obj); 

The obj.review and obj.newProp assignments will result in errors, and the console will display the value { name: "FreeCodeCamp", review: "Awesome" }.

--instructions--

In this challenge you are going to use Object.freeze to prevent mathematical constants from changing. You need to freeze the MATH_CONSTANTS object so that no one is able to alter the value of PI, add, or delete properties.

--hints--

You should not replace the const keyword.

(getUserInput) => assert(getUserInput('index').match(/const/g));

MATH_CONSTANTS should be a constant variable (by using const).

(getUserInput) =>
  assert(getUserInput('index').match(/const\s+MATH_CONSTANTS/g));

You should not change the original declaration of MATH_CONSTANTS.

(getUserInput) =>
  assert(
    getUserInput('index').match(
      /const\s+MATH_CONSTANTS\s+=\s+{\s+PI:\s+3.14\s+};/g
    )
  );

PI should equal 3.14.

assert(PI === 3.14);

--seed--

--seed-contents--

function freezeObj() {
  const MATH_CONSTANTS = {
    PI: 3.14
  };
  // Only change code below this line


  // Only change code above this line
  try {
    MATH_CONSTANTS.PI = 99;
  } catch(ex) {
    console.log(ex);
  }
  return MATH_CONSTANTS.PI;
}
const PI = freezeObj();

--solutions--

function freezeObj() {
  const MATH_CONSTANTS = {
    PI: 3.14
  };
  Object.freeze(MATH_CONSTANTS);

  try {
    MATH_CONSTANTS.PI = 99;
  } catch(ex) {
    console.log(ex);
  }
  return MATH_CONSTANTS.PI;
}
const PI = freezeObj();