Skip to content

Latest commit

 

History

History
167 lines (109 loc) · 9.28 KB

README.md

File metadata and controls

167 lines (109 loc) · 9.28 KB
Raw

Selecting Elements Lab

Introduction

Welcome to your first lab! Please read this entire readme. We'll try to only include information to help you. This way, we won't waste your time and will allow you to get to the coding as fast as possible.

We are going to continue with our search engine that pulls identifying information from Wikipedia. As you remember, Aardvark created a search engine such that when a user asked a question, the program would look to Wikipedia to pull related information about the question topic.

Your task

In the last section, we pulled the header, the text from the first link and the href from the first link. In this section we are going to pull the same information, but from a different simplified Wikipedia page. Since this is a lab we are going to complete our final code in the JavaScript tab of the CodePen below. You will work in the Browser Console to discover what the final solution will be, but to complete the lab, you must put your completed code in the JavaScript Tab of the CodePen.

The rules of the lab

OK, let's explain how to pass this lab, and stick this bad boy on your refrigerator for all the world to see.

<iframe height='482' scrolling='no' title='adele-goldberg-simplified' src='//codepen.io/joemburgess/embed/PmxyNW/?height=482&theme-id=0&default-tab=js,result&embed-version=2&editable=true' frameborder='no' allowtransparency='true' allowfullscreen='true' style='width: 100%;'>See the Pen adele-goldberg-simplified by Joe Burgess (@joemburgess) on CodePen. </iframe>

Go ahead and select the JavaScript tab and you'll see some JavaScript code

//Enter querySelector Code here
var header = document.querySelector('h1').innerHTML
var linkText = document.querySelector('body').querySelector('a').innerHTML
var linkHref = document.querySelector('body').querySelector('a').href

// NO NEED TO MODIFY BELOW HERE
console.log(`The header is: ${header}`)
console.log(`The first link text is: ${linkText}`)
console.log(`The first link href is: ${linkHref}`)

Let's take a look at what is going on.

The first three lines are variable definitions. Variables in JavaScript are just like you remember them in Algebra. They are simply names for some sort of data. The = sign assigns whatever is on the right side to be held inside of whatever is on the left side. With the default code the phrase "ENTER HEADER CODE HERE" is held inside of the header variable.

Open your Console by right clicking in the HTML preview (inside the red square) of the CodePen. From the drop-down, select "Inspect."

Screenshot of Selecting the Console

You should see a console appear at the bottom or on the side (it doesn't matter) of your browser that looks like this:

Screenshot of Selecting the Console

The header is: ENTER HEADER CODE HERE
The first link text is: ENTER LINK TEXT CODE HERE
The first link href is: ENTER LINK HREF CODE HERE

This is outputted by the console.log lines in the CodePen. The CodePen is outputting text to our Browser Console. Here is the code in the JavaScript tab of the CodePen that outputs to the Browser Console.

console.log(`The header is: ${header}`)
console.log(`The first link text is: ${linkText}`)
console.log(`The first link href is: ${linkHref}`)

console.log is a tool we use to output text to our console. Makes sense right? Above I told you that currently the header variable contains "ENTER HEADER CODE HERE". The first console.log looks like this:

console.log(`The header is: ${header}`)

This outputs The header is: ENTER HEADER CODE HERE to the Browser Console. Do you see what happened there? The ${header} took the contents of header and made sure they were sent to the console.

Our task in this lab is to modify the three variables to be the correct querySelector to select the correct elements. You'll know you have selected the correct elements when your Browser Console says:

The header is: Adele Goldberg
The first link text is: computer scientist
The first link href is: https://en.wikipedia.org/wiki/Computer_scientist

All Together Now

We are going to do the first one together, then you'll do the second two on your own. Here is your first task:

Write the querySelector to grab the header, then use innerHTML to grab the contents of the header. You should put that code in the JavaScript tab of the CodePen where it says "ENTER HEADER CODE HERE". Be sure to replace the quotes as well. If everything worked as planned your Browser Console will output The header is: Adele Goldberg

The first variable asks for the querySelector line for the header. Using the same technique you learned in the previous lesson, inspect the element and find out the id attribute of the header. It should be header. Great, now in the Console (be sure to change the top dropdown to CodePen Preview) type document.querySelector("#header"). That should return the correct header. This time though I want just the words "Adele Goldberg". To get just the words in an h1 tag we are going to use the innerHTML attribute.

There are a lot of attributes out there. Don't memorize them, just google around when you can't remember!

Back in the console type:

document.querySelector("#header").innerHTML

That should return "Adele Goldberg". Now, let's get it into our CodePen and make sure the Console is logging correctly.

Modify the first line of code to be:

var header = document.querySelector("#header").innerHTML

Looking at the console, you should see the updated logging.

The header is: Adele Goldberg
The first link text is: ENTER LINK TEXT CODE HERE
The first link href is: ENTER LINK HREF CODE HERE

NOTE: When an error appears in the Chrome JavaScript console, you'll notice that the error message stays visible in the console even after you've modified the code in the CodePen. This isn't necessarily a bad thing, but it can sometimes get a bit confusing if we're working on troubleshooting a new error and a bunch of old error messages are still cluttering up the console. Handily enough, Chrome provides a sweet built-in function, clear(), for clearing the JavaScript console. Simply enter clear() into the Chrome console and everything will disappear, replaced with a Console was cleared message.

As programmers, we need to get familiar with breaking things. In fact, as programmers, our code will spend most of it's life not working until suddenly we get a complex set of interactions right so that it is working. As a programmer thinking of yourself in "broken-land" and rejoicing only when you hit "working-land" will help you and your ego. Think about it: if you're coding while stressing about having moved from "working-land" to "broken-land" you're going to experience stress. Start from the opposite assumption and you're going to spend your days pleasantly surprised!

A key help in moving us from "broken-land" to "working-land" are errors that appear in the Chrome console. Let's start with a common one.

What if we'd changed our code to be like this:

var header = document.querySelector("#personName-header").innerHTML
console.log(header);

If we look in the HTML source, we'll see that there's no element with an id of attribute "personName-header". So our call to querySelector() will return nothing. So if you ask nothing for it's innerHTML attribute, would you expect the browser to say a "broken" thing or a "working" thing?

Try changing your code and see:

Uncaught TypeError: Cannot read property 'innerHTML' of null
    at VM43 pen.js:2

Well null is like nothing. So the browser is telling us it couldn't find the innerHMTL property on null. Does that kind of seem like the error you might have imagined up above?

Errors are our friends, here in "broken-land." Let them guide you.

If you're not sure how to interpret an error, take a look at this comprehensive guide to errors at MDN

On Your Own

You've successfully completed the first question. Now, using what you've learned solve the next two problems:

  1. Using the document.querySelector and text attribute, set the linkText variable to equal the text of the first link, which is "computer scientist". This will be just like you did in the previous README. If done correctly, your console will output the first link text is: computer scientist.
  2. Using the document.querySelector and href attribute, set the linkHref variable to equal the href of the first link, which is "https://en.wikipedia.org/wiki/Computer_scientist". This will also be just like you did in the previous README. If done correctly, your console will output The first link href is: https://en.wikipedia.org/wiki/Computer_scientist.

Good luck!

View Selecting Single Elements Lab on Learn.co and start learning to code for free.