7_FunctionsChallenges.js

// Week 2 - Functions

// In the following exercises, you will need to place your code or answer underneath each
// exercise prompt.

// First try answering these without using references or looking up any information.
// Then, check your answer by using references and/or running your code.
// You can run your JS code using the Chrome or Firefox Developer tools, or by using Node.js or using Replit.com
// Feel free to update your answers if you got them wrong at first -- this exercise is for your own learning.
// But make sure you understand why the correct answer is right.

// Exercise 1. Write a function called prependToString, which accepts two strings.
// The function should return a new string with the second string prepended to the first string.
// Examples:
// prependToString('awesome', 'very') // --> 'veryawesome'
// prependToString('world', 'hello ') // --> 'hello world'
// prependToString('nothing', '') // --> 'nothing'

function prependToString (str1, str2){
  return `${str2}${str1}`;
};

// Exercise 2. Write a function called stringIncludes, which accepts two strings: the first string is a word and the second string is a single character.
// The function should return true if the first string includes the character, otherwise it should return false.
// IMPORTANT: Do not use the built in string.includes() function!
// Examples:
// stringIncludes('awesome', 'e'); // --> true
// stringIncludes('awesome', 'z'); // --> false

function stringIncludes (str, character){
  for (let i = 0; i < str.length; i++){
    if (str[i] === character){
      return true; 
    } 
  }
  return false; 
}

// Exercise 3. Write a function called stringLastIndexOf, which accepts two strings: the first is a word and the second is a single character.
// The function should return the last index at which the character exists or -1 if the character is not found.
// IMPORTANT: Do not use the built in "string".lastIndexOf() function!
// Examples:
// stringLastIndexOf('awesome', 'e'); // --> 6
// stringLastIndexOf('awesome', 'z'); // --> -1

function stringLastIndexOf (word, secondStr){
  for (let i = word.length - 1; i >= 0; i--){
    if (word[i] === secondStr){
      return i; 
    }
  }
  return -1;
}

// Exercise 4. Write a function called removeFromString, which accepts a string, a starting index (number) and a number of characters to remove.
// The function should return a new string with the characters removed.
// Examples:
// removeFromString('Elie', 2, 2) // --> 'El'
// removeFromString('Elie', 0, 1) // --> 'lie'
// removeFromString('Hello School', 0, 6) // --> 'School'
// removeFromString('Hello School', 2, 4) // --> 'HeSchool'
// removeFromString('Hello School', 6, 400) // --> 'Hello '

function removeFromString (string, strIndex, numChar){
  return string.slice(strIndex + numChar)
}
                             
// Exercise 5. Write a function called indexOf, which accepts an array and a number.
// The function should return the first index at which the value exists or -1 if the value is not found.
// IMPORTANT: Do not use the built in array.indexOf() function!
// Examples:
// let arr = [5, 10, 15, 20];
// indexOf(arr, 20); // --> 3
// let arr2 = [1, 2, 3, 4, 5];
// indexOf(arr2, 2); // --> 1
// let arr3 = [1, 2];
// indexOf(arr3, 10); // --> -1

function indexOf (array1, number1){
  for (let i = 0; i < array1.length; i++){
    if (array1[i] === number1){
      return i; 
    }
  } return -1;
}

// Exercise 6. Write a function called includes which accepts a collection, a value, and an optional starting index. The function should return true if the value exists in the collection when we search starting from the starting index. Otherwise, it should return false.
// The collection can be a string, an array, or an object. If the collection is a string or array, the third parameter is a starting index for where to search from. If the collection is an object, the function searches for the value among values in the object; since objects have no sort order, the third parameter is ignored.
// Examples:
// includes([1, 2, 3], 1) // --> true
// includes([1, 2, 3], 1, 2) // --> false
// includes([1, 2, 3], 6) // --> false
// includes({ 'a': 1, 'b': 2 }, 1) // --> true
// includes({ 'a': 1, 'b': 2 }, 'a') // --> false
// includes('abcd', 'b') // --> true
// includes('abcd', 'e') // --> false
// includes('abcd', 'a', 2) // --> false

function includes(collection, value, index) {
  // The line below checks if the collection is an array or a string without an index; 
  if (Array.isArray(collection) || typeof(collection) === 'string'){
    if (index === undefined){
      for (let i = 0; i < collection.length; i++){
        if (collection[i] === value){
          return true; 
        }
      }
  // The line below checks if the collection is an array or a string with an index
    } else if (Array.isArray(collection) || typeof(collection) === 'string') {
      if (collection[index] === value){
        return true; 
      }
    }
    
  }
  // The line below checks if the collection is an object and evaluates whether the object holds the value;  
  else if (typeof(collection) === 'object'){
    for (let key in collection){
      if (collection.hasOwnProperty(key) && collection[key] === value){
        return true; 
      }
    }
  }
  return false; 
}