reading-notes

JavaScript Arrays, Operators, Conditionals, and Loops

Readings

• Arrays
• Operators and Expressions
• Conditionals
• Loops

Arrays

• [ ] designates an Array
• Arrays can carry and value, including additional arrays (multidimensional array)
• .length will return the number of items inside an array
• Items inside an array can be accessed using arrayName[#]
  • Items start at 0
• Multidimensional arrays are accessed using arrayName[#][#]
• Finding items in an array
  • indexOf()
    • Takes an item as an argument and returns the location inside the array, or -1 if the item is not in the array

  const birds = ['Parrot', 'Falcon', 'Owl'];
  console.log(birds.indexOf('Owl'));   //  2
  console.log(birds.indexOf('Rabbit')); // -1
  

• Adding items to an array
  • .push()
    • Takes an item as an argument and pushes it to the end of the array
  • .unshift()
    • Takes an item as an argument and shifts it to the beginning of the array
• Removing items from an array
  • .pop()
    • Pops off the last value in an array
  • .shift()
    • Removes the first value in an array
  • .splice()
    • Takes two arguments
      • First is where to start removing
      • Second is how many to remove

    const cities = ['Manchester', 'Liverpool', 'Edinburgh', 'Carlisle'];
    const index = cities.indexOf('Liverpool');
    if (index !== -1) {
      cities.splice(index, 2);
    }
    console.log(cities);     // [ "Manchester", "Carlisle" ]
  

• Accessing every item
  • of
    • Usually used in conjunction with for
    • Will allow you go through each item in an array in a loop

  const pets = ['cat', 'dog','bird'];
  
  for (const pet of pets) {
    console.log(pet);
   }; // >>Will list out each item in pets
  

  • map()
    • Invokes a function on the items in an array and creates a new array with the results
• Converting between strings and arrays
  • .split()
    • Takes a delimiter as an argument and splits a string into an array
  • .join()
    • Takes a delimiter as an argument and joins items in an array as a string with the delimiter separating the items
  • .toString()
    • Converts an array to a string, but can only use a , as the delimiter

Operators & Expressions

Shorthand Assignment Operators

Name	Shorthand operator	Meaning
Assignment	x = f()	x = f()
Addition assignment	x += f()	x = x + f()
Subtraction assignment	x -= f()	x = x - f()
Multiplication assignment	x *= f()	x = x * f()
Division assignment	x /= f()	x = x / f()
Remainder assignment	x %= f()	x = x % f()
Exponentiation assignment	x **= f()	x = x ** f()
Left shift assignment	x «= f()	x = x « f()
Right shift assignment	x »= f()	x = x » f()
Unsigned right shift assignment	x »>= f()	x = x »> f()
Bitwise AND assignment	x &= f()	x = x & f()
Bitwise XOR assignment	x ^= f()	x = x ^ f()
Bitwise OR assignment	x |= f()	x = x | f()
Logical AND assignment	x &&= f()	x && (x = f()	)
Logical OR assignment	x ||= f()	x || (x = f())
Logical nullish assignment	x ??= f()	x ?? (x = f())