"ECMAScript is a standardized version of JavaScript with the goal of unifying the language's specifications and features. As all major browsers and JavaScript-runtimes follow this specification, the term <i>ECMAScript</i> is interchangeable with the term <i>JavaScript</i>.<br><br>Most of the challenges on freeCodeCamp use the ECMAScript 5 (ES5) specification of the language, finalized in 2009. But JavaScript is an evolving programming language. As features are added and revisions are made, new versions of the language are released for use by developers.<br><br>The most recent standardized version is called ECMAScript 6 (ES6), released in 2015. This new version of the language adds some powerful features that will be covered in this section of challenges, including:<br><br><ul><li>Arrow functions</li><li>Classes</li><li>Modules</li><li>Promises</li><li>Generators</li><li><code>let</code> and <code>const</code></li></ul><br><br><strong>Note</strong><br>Not all browsers support ES6 features. If you use ES6 in your own projects, you may need to use a program (transpiler) to convert your ES6 code into ES5 until browsers support ES6.",
"One of the biggest problems with declaring variables with the <code>var</code> keyword is that you can overwrite variable declarations without an error.",
"As you can see in the code above, the <code>camper</code> variable is originally declared as <code>James</code> and then overridden to be <code>David</code>.",
"In a small application, you might not run into this type of problem, but when your code becomes larger, you might accidently overwrite a variable that you did not intend to overwrite.",
"Because this behavior does not throw an error, searching and fixing bugs becomes more difficult.<br>",
"A new keyword called <code>let</code> was introduced in ES6 to solve this potential issue with the <code>var</code> keyword.",
"If you were to replace <code>var</code> with <code>let</code> in the variable declarations of the code above, the result would be an error.",
"Update the code so it only uses the <code>let</code> keyword.",
"<strong>Note</strong><br>Remember that since <code>let</code> prevents variables from being overridden, you will need to remove one of the declarations entirely."
"When you declare a variable with the <code>var</code> keyword, it is declared globally, or locally if declared inside a function.",
"The <code>let</code> keyword behaves similarly, but with some extra features. When you declare a variable with the <code>let</code> keyword inside a block, statement, or expression, its scope is limited to that block, statement, or expression.",
"<blockquote>var numArray = [];<br>for (var i = 0; i < 3; i++) {<br> numArray.push(i);<br>}<br>console.log(numArray);<br>// returns [0, 1, 2]<br>console.log(i);<br>// returns 3</blockquote>",
"With the <code>var</code> keyword, <code>i</code> is declared globally. So when <code>i++</code> is executed, it updates the global variable. This code is similiar to the following:",
"<blockquote>var numArray = [];<br>var i;<br>for (i = 0; i < 3; i++) {<br> numArray.push(i);<br>}<br>console.log(numArray);<br>// returns [0, 1, 2]<br>console.log(i);<br>// returns 3</blockquote>",
"This behavior will cause problems if you were to create a function and store it for later use inside a for loop that uses the <code>i</code> variable. This is because the stored function will always refer to the value of the updated global <code>i</code> variable.",
"As you can see, <code>printNumTwo()</code> prints 3 and not 2. This is because the value assigned to <code>i</code> was updated and the <code>printNumTwo()</code> returns the global <code>i</code> and not the value <code>i</code> had when the function was created in the for loop. The <code>let</code> keyword does not follow this behavior:",
"<blockquote>'use strict';<br>let printNumTwo;<br>for (let i = 0; i < 3; i++) {<br> if (i === 2) {<br> printNumTwo = function() {<br> return i;<br> };<br> }<br>}<br>console.log(printNumTwo());<br>// returns 2<br>console.log(i);<br>// returns \"i is not defined\"</blockquote>",
"<code>i</code> is not defined because it was not declared in the global scope. It is only declared within the for loop statement. <code>printNumTwo()</code> returned the correct value because three different <code>i</code> variables with unique values (0, 1, and 2) were created by the <code>let</code> keyword within the loop statement.",
"Fix the code so that <code>i</code> declared in the if statement is a separate variable than <code>i</code> declared in the first line of the function. Be certain not to use the <code>var</code> keyword anywhere in your code.",
"This exercise is designed to illustrate the difference between how <code>var</code> and <code>let</code> keywords assign scope to the declared variable. When programming a function similar to the one used in this exercise, it is often better to use different variable names to avoid confusion."
"getUserInput => assert(getUserInput('index').match(/(i\\s*=\\s*).*\\s*.*\\s*.*\\1('|\")block\\s*scope\\2/g), 'message: The variable <code>i</code> declared in the if statement should equal \"block scope\".');",
"<code>let</code> is not the only new way to declare variables. In ES6, you can also declare variables using the <code>const</code> keyword.",
"<code>const</code> has all the awesome features that <code>let</code> has, with the added bonus that variables declared using <code>const</code> are read-only. They are a constant value, which means that once a variable is assigned with <code>const</code>, it cannot be reassigned.",
"As you can see, trying to reassign a variable declared with <code>const</code> will throw an error. You should always name variables you don't want to reassign using the <code>const</code> keyword. This helps when you accidentally attempt to reassign a variable that is meant to stay constant. A common practice is to name your constants in all upper-cases and with an underscore to separate words (e.g. <code>EXAMPLE_VARIABLE</code>).",
"Change the code so that all variables are declared using <code>let</code> or <code>const</code>. Use <code>let</code> when you want the variable to change, and <code>const</code> when you want the variable to remain constant. Also, rename variables declared with <code>const</code> to conform to common practices, meaning constants should be in all caps"
"getUserInput => assert(!getUserInput('index').match(/var/g),'message: <code>var</code> does not exist in code.');",
"getUserInput => assert(getUserInput('index').match(/(const SENTENCE)/g), 'message: <code>SENTENCE</code> should be a constant variable (by using <code>const</code>).');",
"getUserInput => assert(getUserInput('index').match(/(let i)/g), 'message: <code>i</code> should be a variable only defined within the for loop scope (by using<code>let</code>).');"
"Some developers prefer to assign all their variables using <code>const</code> by default, unless they know they will need to reassign the value. Only in that case, they use <code>let</code>.",
"However, it is important to understand that objects (including arrays and functions) assigned to a variable using <code>const</code> are still mutable. Using the <code>const</code> declaration only prevents reassignment of the variable identifier.",
"<blockquote>\"use strict\";<br>const s = [5, 6, 7];<br>s = [1, 2, 3]; // throws error, trying to assign a const<br>s[2] = 45; // works just as it would with an array declared with var or let<br>console.log(s); // returns [5, 6, 45]</blockquote>",
"As you can see, you can mutate the object <code>[5, 6, 7]</code> itself and the variable <code>s</code> will still point to the altered array <code>[5, 6, 45]</code>. Like all arrays, the array elements in <code>s</code> are mutable, but because <code>const</code> was used, you cannot use the variable identifier <code>s</code> to point to a different array using the assignment operator.",
"getUserInput => assert(getUserInput('index').match(/const\\s+s/g), 'message: <code>s</code> should be a constant variable (by using <code>const</code>).');",
"getUserInput => assert(getUserInput('index').match(/const\\s+s\\s*=\\s*\\[\\s*5\\s*,\\s*7\\s*,\\s*2\\s*\\]\\s*;?/g), 'message: Do not change the original array declaration.');",
"As seen in previous challenge, <code>const</code> declaration alone doesn't really protect your data from mutation. To ensure your data doesn't change, JavaScript provides a function <code>Object.freeze</code> to prevent data mutation.",
"Once the object is freezed, you can no longer add/update/delete properties from it. Any attempt at changing the object will be rejected without any error.",
"<blockquote>\nlet obj = {\n name:\"FreeCodeCamp\"\n review:\"Awesome\"\n};\nObject.freeze(obj);\nobj.review = \"bad\"; //will be ignored. Mutation not allowed\nobj.newProp = \"Test\"; // will be ignored. Mutation not allowed\nconsole.log(obj); \n// { name: \"FreeCodeCamp\", review:\"Awesome\"}\n</blockquote>",
"<hr>",
"In this challenge you are going to use <code>Object.freeze</code> to prevent mathematical constants from changing. You need to freeze <code>MATH_CONSTANTS</code> object so that noone is able alter the value of <code>PI</code> or add any more properties to it."
"getUserInput => assert(getUserInput('index').match(/const\\s+MATH_CONSTANTS/g), 'message: <code>MATH_CONSTANTS</code> should be a constant variable (by using <code>const</code>).');",
"getUserInput => assert(getUserInput('index').match(/const\\s+MATH_CONSTANTS\\s+=\\s+{\\s+PI:\\s+3.14\\s+};/g), 'message: Do not change original <code>MATH_CONSTANTS</code>.');",
"In JavaScript, we often don't need to name our functions, especially when passing a function as an argument to another function. Instead, we create inline functions. We don't need to name these functions because we do not reuse them anywhere else.",
"To achieve this, we often use the following syntax:",
"ES6 provides us with the syntactic sugar to not have to write anonymous functions this way. Instead, you can use <strong>arrow function syntax</strong>:",
"When there is no function body, and only a return value, arrow function syntax allows you to omit the keyword <code>return</code> as well as the brackets surrounding the code. This helps simplify smaller functions into one-line statements:",
"Rewrite the function assigned to the variable <code>magic</code> which returns a new <code>Date()</code> to use arrow function syntax. Also make sure nothing is defined using the keyword <code>var</code>."
"getUserInput => assert(getUserInput('index').match(/const\\s+magic/g), 'message: <code>magic</code> should be a constant variable (by using <code>const</code>).');",
"Rewrite the <code>myConcat</code> function which appends contents of <code>arr2</code> to <code>arr1</code> so that the function uses arrow function syntax."
"getUserInput => assert(getUserInput('index').match(/const\\s+myConcat/g), 'message: <code>myConcat</code> should be a constant variable (by using <code>const</code>).');",
"It's time we see how powerful arrow functions are when processing data.",
"Arrow functions work really well with higher order functions, such as <code>map()</code>, <code>filter()</code>, and <code>reduce()</code>, that take other functions as arguments for processing collections of data.",
"We have written this with <code>filter()</code> to at least make it somewhat readable. Now compare it to the following code which uses arrow function syntax instead:",
"Use arrow function syntax to compute the square of only the positive integers (fractions are not integers) in the array <code>realNumberArray</code> and store the new array in the variable <code>squaredIntegers</code>."
"getUserInput => assert(getUserInput('index').match(/const\\s+squaredIntegers/g), 'message: <code>squaredIntegers</code> should be a constant variable (by using <code>const</code>).');",
"assert(Array.isArray(squaredIntegers), 'message: <code>squaredIntegers</code> should be an <code>array</code>');",
"getUserInput => assert(!getUserInput('index').match(/(for)|(while)/g), 'message: loop should not be used');",
"getUserInput => assert(getUserInput('index').match(/map|filter|reduce/g), 'message: <code>map</code>, <code>filter</code>, or <code>reduce</code> should be used');"
"The default parameter kicks in when the argument is not specified (it is undefined). As you can see in the example above, the parameter <code>name</code> will receive its default value <code>\"Anonymous\"</code> when you do not provide a value for the parameter. You can add default values for as many parameters as you want.",
"Modify the function <code>increment</code> by adding default parameters so that it will add 1 to <code>number</code> if <code>value</code> is not specified."
"assert(increment(5, 2) === 7, 'message: The result of <code>increment(5, 2)</code> should be <code>7</code>.');",
"assert(increment(5) === 6, 'message: The result of <code>increment(5)</code> should be <code>6</code>.');",
"getUserInput => assert(getUserInput('index').match(/value\\s*=\\s*1/g), 'message: default parameter <code>1</code> was used for <code>value</code>.');"
"In order to help us create more flexible functions, ES6 introduces the <dfn>rest operator</dfn> for function parameters. With the rest operator, you can create functions that take a variable number of arguments. These arguments are stored in an array that can be accessed later from inside the function.",
"<blockquote>function howMany(...args) {<br> return \"You have passed \" + args.length + \" arguments.\";<br>}<br>console.log(howMany(0, 1, 2)); // You have passed 3 arguments<br>console.log(howMany(\"string\", null, [1, 2, 3], { })); // You have passed 4 arguments.</blockquote>",
"The rest operator eliminates the need to check the <code>args</code> array and allows us to apply <code>map()</code>, <code>filter()</code> and <code>reduce()</code> on the parameters array.",
"assert(sum(0,1,2) === 3, 'message: The result of <code>sum(0,1,2)</code> should be 3');",
"assert(sum(1,2,3,4) === 10, 'message: The result of <code>sum(1,2,3,4)</code> should be 10');",
"assert(sum(5) === 5, 'message: The result of <code>sum(5)</code> should be 5');",
"assert(sum() === 0, 'message: The result of <code>sum()</code> should be 0');",
"getUserInput => assert(getUserInput('index').match(/function\\s+sum\\s*\\(\\s*...args\\s*\\)\\s*{/g), 'message: The <code>sum</code> function uses the <code>...</code> spread operator on the <code>args</code> parameter.');"
"ES6 introduces the <dfn>spread operator</dfn>, which allows us to expand arrays and other expressions in places where multiple parameters or elements are expected.",
"The ES5 code below uses <code>apply()</code> to compute the maximum value in an array:",
"We had to use <code>Math.max.apply(null, arr)</code> because <code>Math.max(arr)</code> returns <code>NaN</code>. <code>Math.max()</code> expects comma-separated arguments, but not an array.",
"The spread operator makes this syntax much better to read and maintain.",
"assert(arr2.every((v, i) => v === arr1[i]), 'message: <code>arr2</code> is correct copy of <code>arr1</code>.');",
"getUserInput => assert(getUserInput('index').match(/\\[\\s*...arr1\\s*\\]/g),'message: <code>...</code> spread operator was used to duplicate <code>arr1</code>.');",
"assert((arr1, arr2) => {arr1.push('JUN'); return arr2.length < arr1.length},'message: <code>arr2</code> remains unchanged when <code>arr1</code> is changed.');"
"We can do something similar with objects as well. <dfn>Destructuring assignment</dfn> is special syntax for neatly assigning values taken directly from an object to variables.",
"Here's the same assignment statement with ES6 destructuring syntax:",
"<blockquote>const { x, y, z } = voxel; // x = 3.6, y = 7.4, z = 6.54</blockquote>",
"If instead you want to store the values of <code>voxel.x</code> into <code>a</code>, <code>voxel.y</code> into <code>b</code>, and <code>voxel.z</code> into <code>c</code>, you have that freedom as well.",
"assert(typeof getLength('') === 'number', 'message: the function <code>getLength()</code> returns a number.');",
"assert(getLength(\"FreeCodeCamp\") === 12, 'message: <code>getLength(\"FreeCodeCamp\")</code> should be <code>12</code>');",
"getUserInput => assert(getUserInput('index').match(/\\{\\s*length\\s*:\\s*len\\s*}\\s*=\\s*str/g),'message: destructuring with reassignment was used');"
"One key difference between the spread operator and array destructuring is that the spread operator unpacks all contents of an array into a comma-separated list. Consequently, you cannot pick or choose which elements you want to assign to variables.",
"Use destructuring assignment to swap the values of <code>a</code> and <code>b</code> so that <code>a</code> receives the value stored in <code>b</code>, and <code>b</code> receives the value stored in <code>a</code>."
"assert(a === 6, 'message: Value of <code>a</code> should be 6, after swapping.');",
"assert(b === 8, 'message: Value of <code>b</code> should be 8, after swapping.');",
"// assert(/\\[\\s*(\\w)\\s*,\\s*(\\w)\\s*\\]\\s*=\\s*\\[\\s*\\2\\s*,\\s*\\1\\s*\\]/g.test(code), 'message: Use array destructuring to swap a and b.');"
"Variables <code>a</code> and <code>b</code> take the first and second values from the array. After that, because of rest operator's presence, <code>arr</code> gets rest of the values in the form of an array.",
"The rest element only works correctly as the last variable in the list. As in, you cannot use the rest operator to catch a subarray that leaves out last element of the original array.",
"<hr>",
"Use destructuring assignment with the rest operator to perform an effective <code>Array.prototype.slice()</code> so that <code>arr</code> is a sub-array of the original array <code>source</code> with the first two elements ommitted."
"In some cases, you can destructure the object in a function argument itself.",
"Consider the code below:",
"<blockquote>const profileUpdate = (profileData) => {<br> const { name, age, nationality, location } = profileData;<br> // do something with these variables<br>}</blockquote>",
"This effectively destructures the object sent into the function. This can also be done in-place:",
"<blockquote>const profileUpdate = ({ name, age, nationality, location }) => {<br> /* do something with these fields */<br>}</blockquote>",
"This removes some extra lines and makes our code look neat.",
"This has the added benefit of not having to manipulate an entire object in a function; only the fields that are needed are copied inside the function.",
"<hr>",
"Use destructuring assignment within the argument to the function <code>half</code> to send only <code>max</code> and <code>min</code> inside the function."
"A new feature of ES6 is the <dfn>template literal</dfn>. This is a special type of string that allows you to use string interpolation features to create strings.",
"Consider the code below:",
"<blockquote>const person = {<br> name: \"Zodiac Hasbro\",<br> age: 56<br>};<br><br>// string interpolation<br>const greeting = `Hello, my name is ${person.name}!<br>I am ${person.age} years old.`;<br><br>console.log(greeting); // prints<br>// Hello, my name is Zodiac Hasbro!<br>// I am 56 years old.<br></blockquote>",
"A lot of things happened there.",
"Firstly, the <code>${variable}</code> syntax used above is a place holder. Basically, you won't have to use concatenation with the <code>+</code> operator anymore. To add variables to strings, you just drop the variable in a template string and wrap it with <code>${</code> and <code>}</code>.",
"Secondly, the example uses backticks (<code>`</code>), not quotes (<code>'</code> or <code>\"</code>), to wrap the string. Notice that the string is multi-line.",
"This new way of creating strings gives you more flexibility to create robust strings.",
"Use template literal syntax with backticks to display each entry of the <code>result</code> object's <code>failure</code> array. Each entry should be wrapped inside an <code>li</code> element with the class attribute <code>text-warning</code>, and listed within the <code>resultDisplayArray</code>."
"assert(typeof makeList(result.failure) === 'object' && resultDisplayArray.length === 3, 'message: <code>resultDisplayArray</code> is a list containing <code>result failure</code> messages.');",
"assert(makeList(result.failure).every((v, i) => v === `<li class=\"text-warning\">${result.failure[i]}</li>`), 'message: <code>resultDisplayArray</code> is the desired output.');",
"getUserInput => assert(getUserInput('index').match(/\\`<li class=\"text-warning\">\\$\\{\\w+\\}<\\/li>\\`/g), 'message: Template strings were used');"
"<code>getMousePosition</code> is a simple function that returns an object containing two fields.",
"ES6 provides the syntactic sugar to eliminate the redundancy of having to write <code>x: x</code>. You can simply write <code>x</code> once, and it will be converted to<code>x: x</code> (or something equivalent) under the hood.",
"Here is the same function from above rewritten to use this new syntax:",
"<blockquote>const getMousePosition = (x, y) => ({ x, y });</blockquote>",
"<hr>",
"Use simple fields with object literals to create and return a <code>Person</code> object."
"When defining functions within objects in ES5, we have to use the keyword <code>function</code> as follows:",
"<blockquote>const person = {<br> name: \"Taylor\",<br> sayHello: function() {<br> return `Hello! My name is ${this.name}.`;<br> }<br>};</blockquote>",
"With ES6, You can remove the <code>function</code> keyword and colon altogether when defining functions in objects. Here's an example of this syntax:",
"<blockquote>const person = {<br> name: \"Taylor\",<br> sayHello() {<br> return `Hello! My name is ${this.name}.`;<br> }<br>};</blockquote>",
"<hr>",
"Refactor the function <code>setGear</code> inside the object <code>bicycle</code> to use the shorthand syntax described above."
"assert(() => { bicycle.setGear(48); return bicycle.gear === 48 }, 'message: <code>setGear</code> is a function and changes the <code>gear</code> variable.');",
"getUserInput => assert(!getUserInput('index').match(/:\\s*function\\s*\\(\\)/g), 'message: Declarative function was used.');"
"ES6 provides a new syntax to help create objects, using the keyword <dfn>class</dfn>.",
"This is to be noted, that the <code>class</code> syntax is just a syntax, and not a full-fledged class based implementation of object oriented paradigm, unlike in languages like Java, or Python, or Ruby etc.",
"In ES5, we usually define a constructor function, and use the <code>new</code> keyword to instantiate an object.",
"<blockquote>var SpaceShuttle = function(targetPlanet){<br> this.targetPlanet = targetPlanet;<br>}<br>var zeus = new spaceShuttle('Jupiter');</blockquote>",
"<blockquote>class SpaceShuttle {<br> constructor(targetPlanet){<br> this.targetPlanet = targetPlanet;<br> }<br>}<br>const zeus = new spaceShuttle('Jupiter');</blockquote>",
"Notice that the <code>class</code> keyword declares a new function, and a constructor was added, which would be invoked when <code>new</code> is called - to create a new object.",
"<hr>",
"Use <code>class</code> keyword and write a proper constructor to create the <code>Vegetable</code> class.",
"The <code>Vegetable</code> lets you create a vegetable object, with a property <code>name</code>, to be passed to constructor."
"assert(typeof Vegetable === 'function' && typeof Vegetable.constructor === 'function', 'message: <code>Vegetable</code> should be a <code>class</code> with a defined <code>constructor</code> method.');",
"Getter functions are meant to simply return (get) the value of an object's private variable to the user without the user directly accessing the private variable.",
"Setter functions are meant to modify (set) the value of an object's private variable based on the value passed into the setter function. This change could involve calculations, or even overwriting the previous value completely.",
"Remember that <code>C = 5/9 * (F - 32)</code> and <code>F = C * 9.0 / 5 + 32</code>, where F is the value of temperature in Fahrenheit scale, and C is the value of the same temperature in Celsius scale",
"assert(typeof Thermostat === 'function' && typeof Thermostat.constructor === 'function','message: <code>Thermostat</code> should be a <code>class</code> with a defined <code>constructor</code> method.');",
"assert(() => {const t = new Thermostat(32); return typeof t === 'object' && t.temperature === 0;}, 'message: <code>Thermostat</code> can be instantiated.');"
"In the past, the function <code>require()</code> would be used to import the functions and code in external files and modules. While handy, this presents a problem: some files and modules are rather large, and you may only need certain code from those external resources.",
"ES6 gives us a very handy tool known as <dfn>import</dfn>. With it, we can choose which parts of a module or file to load into a given file, saving time and memory.",
"Consider the following example. Imagine that <code>math_array_functions</code> has about 20 functions, but I only need one, <code>countItems</code>, in my current file. The old <code>require()</code> approach would force me to bring in all 20 functions. With this new <code>import</code> syntax, I can bring in just the desired function, like so:",
"<blockquote>import { countItems } from \"math_array_functions\"</blockquote>",
"<strong>Note</strong><br>The whitespace surrounding the function inside the curly braces is a best practice - it makes it easier to read the <code>import</code> statement.",
"<strong>Note</strong><br>The lessons in this section handle non-browser features. <code>import</code>, and the statements we introduce in the rest of these lessons, won't work on a browser directly. However, we can use various tools to create code out of this to make it work in browser.",
"<strong>Note</strong><br>In most cases, the file path requires a <code>./</code> before it; otherwise, node will look in the <code>node_modules</code> directory first trying to load it as a dependencie.",
"Add the appropriate <code>import</code> statement that will allow the current file to use the <code>capitalizeString</code> function. The file where this function lives is called <code>\"string_functions\"</code>, and it is in the same directory as the current file."
"In the previous challenge, you learned about <code>import</code> and how it can be leveraged to import small amounts of code from large files. In order for this to work, though, we must utilize one of the statements that goes with <code>import</code>, known as <dfn>export</dfn>. When we want some code - a function, or a variable - to be usable in another file, we must export it in order to import it into another file. Like <code>import</code>, <code>export</code> is a non-browser feature.",
"The following is what we refer to as a <dfn>named export</dfn>. With this, we can import any code we export into another file with the <code>import</code> syntax you learned in the last lesson. Here's an example:",
"Below are two variables that I want to make available for other files to use. Utilizing the first way I demonstrated <code>export</code>, export the two variables."
"Suppose you have a file that you wish to import all of its contents into the current file. This can be done with the <dfn>import *</dfn> syntax.",
"Here's an example where the contents of a file named <code>\"math_functions\"</code> are imported into a file in the same directory:",
"<blockquote>import * as myMathModule from \"math_functions\"<br>myMathModule.add(2,3);<br>myMathModule.subtract(5,3);</blockquote>",
"And breaking down that code:",
"<blockquote>import * as object_with_name_of_your_choice from \"file_path_goes_here\"<br>object_with_name_of_your_choice.imported_function</blockquote>",
"You may use any name following the <code>import * as </code>portion of the statement. In order to utilize this method, it requires an object that receives the imported values. From here, you will use the dot notation to call your imported values.",
"The code below requires the contents of a file, <code>\"capitalize_strings\"</code>, found in the same directory as it, imported. Add the appropriate <code>import *</code> statement to the top of the file, using the object provided."
"In the <code>export</code> lesson, you learned about the syntax referred to as a <dfn>named export</dfn>. This allowed you to make multiple functions and variables available for use in other files.",
"There is another <code>export</code> syntax you need to know, known as <dfn>export default</dfn>. Usually you will use this syntax if only one value is being exported from a file. It is also used to create a fallback value for a file or module.",
"Here is a quick example of <code>export default</code>:",
"<blockquote>export default function add(x,y) {<br> return x + y;<br>}</blockquote>",
"Note: Since <code>export default</code> is used to declare a fallback value for a module or file, you can only have one value be a default export in each module or file. Additionally, you cannot use <code>export default</code> with <code>var</code>, <code>let</code>, or <code>const</code>",
"getUserInput => assert(getUserInput('index').match(/export\\s+default\\s+function\\s+subtract\\(x,y\\)\\s+{return\\s+x\\s-\\s+y;}/g), 'message: Proper used of <code>export</code> fallback.');"
"In the last challenge, you learned about <code>export default</code> and its uses. It is important to note that, to import a default export, you need to use a different <code>import</code> syntax.",
"In the following example, we have a function, <code>add</code>, that is the default export of a file, <code>\"math_functions\"</code>. Here is how to import it:",
"<blockquote>import add from \"math_functions\";<br>add(5,4); //Will return 9</blockquote>",
"The syntax differs in one key place - the imported value, <code>add</code>, is not surrounded by curly braces, <code>{}</code>. Unlike exported values, the primary method of importing a default export is to simply write the value's name after <code>import</code>.",
"<hr>",
"In the following code, please import the default export, <code>subtract</code>, from the file <code>\"math_functions\"</code>, found in the same directory as this file."
