Basic Data Structures: Check For The Presence of an Element With indexOf()

Days: 45-47

Since arrays can be changed, or mutated, at any time, there's no guarantee about where a particular piece of data will be on a given array, or if that element even still exists. Luckily, JavaScript provides us with another built-in method, indexOf(), that allows us to quickly and easily check for the presence of an element on an array. indexOf() takes an element as a parameter, and when called, it returns the position, or index, of that element, or -1 if the element does not exist on the array.

For example:

let fruits = ['apples', 'pears', 'oranges', 'peaches', 'pears'];

fruits.indexOf('dates') // returns -1
fruits.indexOf('oranges') // returns 2
fruits.indexOf('pears') // returns 1, the first index at which the element exists

indexOf() can be incredibly useful for quickly checking for the presence of an element on an array. We have defined a function, quickCheck, that takes an array and an element as arguments. Modify the function using indexOf() so that it returns true if the passed element exists on the array, and false if it does not.

Prevent Infinite Loops with a Valid Terminal Condition

Debugging: Prevent Infinite Loops with a Valid Terminal Condition

The final topic is the dreaded infinite loop. Loops are great tools when you need your program to run a code block a certain number of times or until a condition is met, but they need a terminal condition that ends the looping. Infinite loops are likely to freeze or crash the browser, and cause general program execution mayhem, which no one wants.

There was an example of an infinite loop in the introduction to this section - it had no terminal condition to break out of the while loop inside loopy(). Do NOT call this function!

function loopy() {
  while(true) {
    console.log("Hello, world!");
  }
}
It's the programmer's job to ensure that the terminal condition, which tells the program when to break out of the loop code, is eventually reached. One error is incrementing or decrementing a counter variable in the wrong direction from the terminal condition. Another one is accidentally resetting a counter or index variable within the loop code, instead of incrementing or decrementing it.


The myFunc() function contains an infinite loop because the terminal condition i != 4 will never evaluate to false (and break the looping) - i will increment by 2 each pass, and jump right over 4 since i is odd to start. Fix the comparison operator in the terminal condition so the loop only runs for i less than or equal to 4.

Accessing Nested Arrays

As we have seen in earlier examples, objects can contain both nested objects and nested arrays. Similar to accessing nested objects, Array bracket notation can be chained to access nested arrays.

Here is an example of how to access a nested array:

var ourPets = [
  {
    animalType: "cat",
    names: [
      "Meowzer",
      "Fluffy",
      "Kit-Cat"
    ]
  },
  {
    animalType: "dog",
    names: [
      "Spot",
      "Bowser",
      "Frankie"
    ]
  }
];
ourPets[0].names[1]; // "Fluffy"
ourPets[1].names[0]; // "Spot"

Retrieve the second tree from the variable myPlants using object dot and array bracket notation.

Basic JavaScript: Return a Value from a Function with Return

We can pass values into a function with arguments. You can use a return statement to send a value back out of a function.

Example

function plusThree(num) {

  return num + 3;

}

var answer = plusThree(5); // 8

plusThree takes an argument for num and returns a value equal to num + 3.

Create a function timesFive that accepts one argument, multiplies it by 5, and returns the new value. See the last line in the editor for an example of how you can test your timesFive function.

Escaping Literal Quotes in Strings: #100days of code D27

When you are defining a string you must start and end with a single or double quote. What happens when you need a literal quote: "or 'inside of your string?

In JavaScript, you can escape a quote from considering it as an end of string quote by placing a backslash (\) in front of the quote.

var sampleStr = "Alan said, \"Peter is learning JavaScript\".";

This signals to JavaScript that the following quote is not the end of the string, but should instead appear inside the string. So if you were to print this to the console, you would get:

Alan said, "Peter is learning JavaScript".

---

Use backslashes to assign a string to the myStrvariable so that if you were to print it to the console, you would see:

I am a "double quoted" string inside "double quotes".

1st #freecodcamp Certification is in the bag...

Long over due, after a few starts and long pauses. One down 5 to go.

#FreeCodeCamp Change Text with Click Events

#FreeCodeCamp Change Text with Click Events

When our click event happens, we can use jQuery to update an HTML element.

Let's make it so that when a user clicks the "Get Message" button, we change the text of the element with the class message to say "Here is the message".

We can do this by adding the following code within our click event:

$(".message").html("Here is the message");