JS Muscle Memory

This problem set will test your understanding of how JavaScript is evaluated. Check your answers by running the lines code. Type out these expressions and avoid copy & paste. Get used to typing JavaScript! Some of these answers are obvious but run the code anyway to get familiar with the workflow for running JavaScript.

Task 1

Predict what the following JavaScript expressions will evaluate to.

• Complete all of these inside of the Chrome DevTools

4 + 4 / 2
(2 + -7) * 3
101 % 10
12 - 4 % 3
true && false
true && !(false || false)
!true && !(false || false)
'cat' + 'dog'
2 + 'pizza'
2.5 * 'fish'
5 >= 11
5 === 5.0
7 !== 7.1
5 + 5 > 8
6 + 6 !== 12
2 > 1 || false
'true' === true
10 % 2 === 0
21 % 2 === 0
21 % 2 !== 0
21 % 2 === 1
12 % 3 === 0
9 % 3 === 0
14 % 3 === 0
'new york'[0]
'new york'[1]
'san francisco'[2 * 3]
'engineering'[3].toUpperCase()
'engineering'.indexOf('G')
'engineering'.indexOf('neer')
'engineering'.indexOf('r') > -1
'science'.indexOf('x') === -1

Task 2

Predict what the console.log lines will print out. Test your work by writing these code snippets to .js files and running them. Put each snippet into it's own .js file and see what the console.logs print out. Reference the running_javascript reading for how to run .js files.

// 1
let idx = 'abcde'.indexOf('D');
idx = idx + 11;
console.log(idx); // ?
idx * 2;
console.log(idx); // ?

// 2
let num = 33;
let isEven = num % 2 === 0;
console.log(isEven); // ?
console.log(!isEven); // ?

// 3
let str1 = 'marker';
let num = 'whiteboard'.length - str1.length;
console.log(num); // ?
let str2 = 'bootcamp';
console.log(str2[num].toUpperCase()); // ?
let char = str2[num].toLowerCase(); // ?
console.log(char + '!'); // ?

// 4
let sentence = 'welcome to bootcamp prep';
let lastChar = sentence[sentence.length - 1];
console.log(lastChar); // ?
console.log(sentence.indexOf(lastChar)); // ?

Task 3: Conditionals

Predict what will happen in the following examples. Which console.logs will actually print? To check your work, type these code snippets to .js files. No copy and pasting! After, feel free to play around with the variable (by assigning your own value) in each example to experiment!

// 5
let age = 30; // try different numbers here
if (age > 30) {
  console.log('older than 30');
} else {
  console.log('younger than 30');
}

// 6
let str = 'pizza'; // try different strings here
if (str.length > 10) {
  console.log('long string');
} else {
  console.log('short string');
}
if (str[0] === 'p') {
  console.log('starts with p');
}

// 7
let num = 15; // try different numbers here
if (num % 3 === 0) {
  console.log('divisible by 3');
} else if (num % 5 === 0) {
  console.log('divisible by 5');
}

// 8
let num = 15; // try different numbers here
if (num % 3 === 0) {
  console.log('divisible by 3');
}
if (num % 5 === 0) {
  console.log('divisible by 5');
}

// 9
let str = 'General Assembly'; // try different strings here
if (str[0] === str[0].toUpperCase()) {
  console.log('starts with a capital!');
}
if (str[str.length - 1] === str[str.length - 1].toUpperCase()) {
  console.log('ends with a capital!');
}

// 10
let num = -44; // try different numbers here
if (num > 0) {
  console.log('positive');
} else if (num < 0) {
  console.log('negative');
} else {
  console.log(0);
}
if (num % 2 === 0) {
  console.log('even');
} else {
  console.log('odd');
}

Task 4: Conditional Muscle Memory

Practice typing the syntax for conditionals. Type each snippet 10 times each to burn the muscle memory into your typing fingers! Be sure to use proper spacing and indentation, type it exactly as shown below. Run the code after each time to make sure it runs. You'll realize how easy it is to forget parentheses or braces. Syntax errors like this will cause your code to be totally misunderstood by the computer. Practice, practice, practice!

let num = 11; // feel free to change the value of this variable
if (num > 5) {
  console.log('if');
}

let num = 5; // feel free to change the value of this variable
if (num > 5) {
  console.log('if');
} else {
  console.log('else');
}

let num = 0; // feel free to change the value of this variable
if (num < 0) {
  console.log('if');
} else if (num > 0) {
  console.log('else if');
} else {
  console.log('else');
}

Task 5: Function Muscle Memory

Practice typing the syntax for functions. Type each snippet 10 times. Focus on using proper style and indentation. Be sure to test your code by running it after each repetition. You'll be surprised and also annoyed at what details you missed! Learn from those typos.

function sayHello(name) {
  let msg = 'Hello, ' + name + '. How are you?';
  return msg;
}
console.log(sayHello('bootcamp prep')); // feel free to change the string being passed

function checkNumber(num) {
  if (num > 0) {
    return 'positive';
  } else if (num < 0) {
    return 'negative';
  } else {
    return 'zero';
  }
}
console.log(checkNumber(5)); // feel free to change the number being passed

function fizzBuzz1(max) {
  for (let i = 0; i < max; i += 1) {

    if (i % 3 === 0 && i % 5 !== 0) {
      console.log(i);
    } else if (i % 5 === 0 && i % 3 !== 0) {
      console.log(i);
    }
  }
}

function evenCaps(sentence) {
  let newSentence = "";

  for (let i = 0; i < sentence.length; i++) {
    let char = sentence[i];

    if (i % 2 === 0) {
      let capitalChar = char.toUpperCase();
      newSentence += capitalChar;
    } else {
      newSentence += char;
    }
  }

  return newSentence;
}

Tasks 6: Complete all JavaScript Problems

• 1-tripler.js
• 2-odd-range.js
• 3-is-prime.js
• 4-cat-builder.js
• 5-value-pairs.js
• 6-does-key-exists.js
• 7-adults.js
• 8-count-scores.js
• 9-decomposition.js