4. String Methods & Conditional Statements

Follow along with code examples here!

Table of Contents:

A string of characters is like a bracelet with beads on it

Summary

  • Strings are sequences of characters enclosed in quotes. You can access individual characters using bracket notation and check their length with .length. Strings are immutable, meaning their characters cannot be changed directly.

  • String methods like includes, startsWith, endsWith, indexOf, slice, toUpperCase, and replace allow you to search, analyze, and manipulate string data.

  • Conditional statements (if, else if, else) let you control the flow of your program based on data values. The order of conditions matters, and only the first true condition in a chain will execute.

  • Guard clauses are single if statements that return early from a function, simplifying conditional logic.

  • Ternary operators provide a concise way to choose between two values based on a condition.

Strings

A string is a sequence of characters between single or double quotations.

console.log("This is a string!");
console.log('!@#$%^&*()1234556'); // <-- also a string

Escaping Characters

If you want to use quotation marks in your string, you have to "escape" them by putting a \ in front.

console.log("The robot said, \"beep boop bop\"");
// Output: The robot said "beep boop bop"

There are many other characters that you can use the escape character (\) such as the "tab" character (\t) and the "newline" character (\n):

console.log("hello\tworld");
// Output: hello  world

console.log("First line\nSecond line");
// Output: First line
// Output: Second line

String Interpolation

When used within backticks, an expression can be interpolated into a string for easy formatting:

console.log(`The sum of 10 and 2 is ${10 + 2}`);
// Output: The sum of 10 and 2 is 12

String Indexes and Bracket Notation

Each character in a string, including spaces, has an index — a numbered position starting at 0.

We can get a single character from a string using Bracket Notation and the index: string[index]

console.log("abc"[0]);    // Output: a
console.log("abc"[1]);    // Output: b
console.log("abc"[2]);    // Output: c

It works on variables too!

const message = 'Hello there!';

console.log(message[0]);  // Output: H
console.log(message[4]);  // Output: o
console.log(message[5]);  // Output: ???
console.log(message[11]); // Output: ???

If you use bracket notation and there is no character at the given index, undefined will be returned:

const message = 'Hello there!';

console.log(message[50]); // Output: undefined

Strings are Immutable

  • Strings are "immutable" (unable to be mutated). In other words, you cannot use bracket notation to change characters of a string.

  • If you try, no error will be thrown, nothing will happen.

const message = 'Hello there!';

// Nothing will happen if you attempt to mutate a string.
message[0] = "J";

console.log(message); // Output: "Hello there!"

String Length

Every string also has a length property that is accessed using dot notation: string.length

It tells us the number of characters in a string (including spaces). When combined with bracket notation, it can be useful for counting indexes backwards from the end of a string.

const message = 'Hello there!';

console.log(message.length);
// Output: 12

console.log(message[message.length - 1]);
// Output: ! 

console.log(message[message.length - 2]);
// Output: ???

console.log(message[message.length - 12]);
// Output: ???

String Methods

A method is a function that is attached to a value. Often, methods are used to manipulate the value they are attached to.

  • Methods are invoked using dot notation: value.method()

First, let's look at some "read only" string methods that return a boolean: includes, startsWith, endsWith,

const fruits = 'apples, bananas, cherries';

console.log(fruits.includes('ana'))
// Output: true

console.log(fruits.includes('ANA'))
// Output: false

console.log(fruits.startsWith('apple'))
// Output: true

console.log(fruits.endsWith('s'))
// Output: true

The methods indexOf, lastIndexOf return a number representing the index of a particular character we're looking for:

const fruits = 'apples, bananas, cherries';

console.log(fruits.indexOf('p'))
// Output: 1

console.log(fruits.lastIndexOf('p'))
// Output: 2

console.log(fruits.indexOf('z'))
// Output: -1 (not found)

When combined, these methods can be used in clever ways!

const hasOnlyOne = (str, letter) => {
  return str.indexOf(letter) === str.lastIndexOf(letter);
}
console.log(hasOnlyOne('hello', 'h'))
// Output: true

console.log(hasOnlyOne('hello', 'l'))
// Output: false

The following methods return a copy of a string modified in some way: slice, toUpperCase, toLowerCase, repeat, replace, replaceAll

const fruits = 'apples, bananas, cherries';

const apples = fruits.slice(0, 6);
console.log(apples);
// Output: apples

const loudFruits = fruits.toUpperCase()
console.log(loudFruits);
// Output: APPLES, BANANAS, CHERRIES

console.log(apples.repeat(3));
// Output: applesapplesapples

console.log(apples.replace('p', 'g'));
// Output: agples

console.log(apples.replaceAll('p', 'g'));
// Output: aggles

Conditional Statements

Conditional statements allow us to change the behavior of our programs based on the current values of our data.

In a decision tree, depending on the conditions, we can make different decisions.
Q: In the decision tree above, what are the variables that will impact the end result?

The first variable is the weather and then, depending on the weather, the variable time or hungry is used to determine whether to walk or take the bus.

if/else if/else statements

To define the possible decisions that our program can make, we use if, else if, and else statements:

const isItHot = (temp) => {
  if (temp > 100) {
    console.log("So Hot!")
  } else if (temp > 90) {
    console.log("Yes!")
  } else if (temp > 75) {
    console.log("Eh")
  } else {
    console.log("Nah")
  }
}
isItHot(80);
// Output: Eh

isItHot(95);
// Output: Yes!

isItHot(105);
// Output: So Hot!

isItHot(60);
// Output: Nah

  • if and else if statements require a boolean condition to evaluate to true in order to run

  • There can be many else if statements, or none at all.

  • else statements do not require a condition and will run only when none of the other options do.

Order Matters

Only the first condition that is true will be executed. This means we have to be careful with the order in which we write our conditional statements.

Q: What happens if we rearrange the conditional statements like so?

const isItHot = (temp) => {
  if (temp > 75) {
    console.log("Eh")
  } else if (temp > 90) {
    console.log("Yes!")
  } else if (temp > 100) {
    console.log("So Hot!")
  } else {
    console.log("Nah")
  }
}
isItHot(80);
// Output: ???

isItHot(95);
// Output: ???

isItHot(105);
// Output: ???

isItHot(60);
// Output: ???

Only if statements

In an if/else if/else chain of conditional statements, only one statement will be executed. But what if we replace all of the else if and else statements with other if statements?

const isItHot = (temp) => {
  if (temp > 75) {
    console.log("Eh")
  } 
  if (temp > 90) {
    console.log("Yes!")
  }
  if (temp > 100) {
    console.log("So Hot!")
  }
  if (temp <= 75) {
    console.log("Nah")
  }
}

isItHot(105);
// Output: ???

Guard Clauses

When working with a function that changes the value returned based on a condition, we can avoid using conditional chains and only use if statements called "guard clauses".

A guard clause is an if statement that returns before subsequent return statements have a chance to be executed.

const isItHot = (temp) => {
  if (temp > 75) {
    return "Eh";
  }
  if (temp > 90) {
    return "Yes!";
  }
  if (temp > 100) {
    return "So Hot!";
  }
  return "Nah";
}

console.log(isItHot(105));
// Output: ???
Q: Why doesn't the last return statement need an if statement?

If the program makes it to the last return "Nah" statement, we can assume that the temperature is less than or equal to 75 because none of the other conditions were true.

Use Ternary Operators To Simplify Conditionals

  • if and else statements let you choose between one of two code blocks to execute.

  • The ternary operator condition ? valA : valB is used to choose between one of two values.

// Okay - Use an If statement to choose which code block to execute
const isThisEven = (num) => {
  let message;
  if (num % 2 === 0) {
    message = 'it is even!';
  } else {
    message = 'it is odd!';
  }
  console.log(message);
}

// Better - Use a ternary to choose which value to assign to message
const isThisEven = (num) => {
  const message = num % 2 === 0 ? "it is even!" : "it is odd!";
  console.log(message);
}
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