freeCodeCamp/curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-javascript/accessing-object-properties-with-variables.english.md

id, title, challengeType, isHidden, videoUrl, forumTopicId

id	title	challengeType	isHidden	videoUrl	forumTopicId
56533eb9ac21ba0edf2244c9	Accessing Object Properties with Variables	1	false	https://scrimba.com/c/cnQyKur	16165

Description

Another use of bracket notation on objects is to access a property which is stored as the value of a variable. This can be very useful for iterating through an object's properties or when accessing a lookup table. Here is an example of using a variable to access a property:

var dogs = {
  Fido: "Mutt",  Hunter: "Doberman",  Snoopie: "Beagle"
};
var myDog = "Hunter";
var myBreed = dogs[myDog];
console.log(myBreed); // "Doberman"

Another way you can use this concept is when the property's name is collected dynamically during the program execution, as follows:

var someObj = {
  propName: "John"
};
function propPrefix(str) {
  var s = "prop";
  return s + str;
}
var someProp = propPrefix("Name"); // someProp now holds the value 'propName'
console.log(someObj[someProp]); // "John"

Note that we do not use quotes around the variable name when using it to access the property because we are using the value of the variable, not the name.

Instructions

Use the playerNumber variable to look up player 16 in testObj using bracket notation. Then assign that name to the player variable.

Tests

tests:
  - text: <code>playerNumber</code> should be a number
    testString: assert(typeof playerNumber === 'number');
  - text: The variable <code>player</code> should be a string
    testString: assert(typeof player === 'string');
  - text: The value of <code>player</code> should be "Montana"
    testString: assert(player === 'Montana');
  - text: You should use bracket notation to access <code>testObj</code>
    testString: assert(/testObj\s*?\[.*?\]/.test(code));
  - text: You should not assign the value <code>Montana</code> to the variable <code>player</code> directly.
    testString: assert(!code.match(/player\s*=\s*"|\'\s*Montana\s*"|\'\s*;/gi));
  - text: You should be using the variable <code>playerNumber</code> in your bracket notation
    testString: assert(/testObj\s*?\[\s*playerNumber\s*\]/.test(code));

Challenge Seed

// Setup
var testObj = {
  12: "Namath",
  16: "Montana",
  19: "Unitas"
};

// Only change code below this line

var playerNumber;       // Change this line
var player = testObj;   // Change this line

After Test

if(typeof player !== "undefined"){(function(v){return v;})(player);}

Solution

var testObj = {
  12: "Namath",
  16: "Montana",
  19: "Unitas"
};
var playerNumber = 16;
var player = testObj[playerNumber];